diff --git a/java/res/values-km-rKH/strings.xml b/java/res/values-km-rKH/strings.xml
index 4d7de93..519aa44 100644
--- a/java/res/values-km-rKH/strings.xml
+++ b/java/res/values-km-rKH/strings.xml
@@ -29,7 +29,7 @@
     <string name="popup_on_keypress" msgid="123894815723512944">"លេច​ឡើង​នៅ​​ពេល​ចុច​គ្រាប់​ចុច"</string>
     <string name="general_category" msgid="1859088467017573195">"ទូទៅ"</string>
     <string name="correction_category" msgid="2236750915056607613">"ការ​កែ​អត្ថបទ"</string>
-    <string name="gesture_typing_category" msgid="497263612130532630">"បញ្ចូល​ដោយ​ប្រើ​កាយវិការ​"</string>
+    <string name="gesture_typing_category" msgid="497263612130532630">"បញ្ចូល​ដោយ​ប្រើ​កាយវិការ"</string>
     <string name="misc_category" msgid="6894192814868233453">"ជម្រើស​ផ្សេងទៀត"</string>
     <string name="advanced_settings" msgid="362895144495591463">"ការ​កំណត់​កម្រិត​ខ្ពស់"</string>
     <string name="advanced_settings_summary" msgid="4487980456152830271">"ជម្រើស​សម្រាប់​អ្នក​ជំនាញ"</string>
@@ -39,7 +39,7 @@
     <string name="show_language_switch_key_summary" msgid="7343403647474265713">"បង្ហាញ​នៅ​ពេល​ដែល​បើក​ភាសា​បញ្ចូល​ច្រើន"</string>
     <string name="sliding_key_input_preview" msgid="6604262359510068370">"បង្ហាញ​ទ្រនិច​បង្ហាញ​ស្លាយ"</string>
     <string name="sliding_key_input_preview_summary" msgid="6340524345729093886">"បង្ហាញ​​សញ្ញា​មើល​​ឃើញ​ខណៈ​ពេល​ដែល​រុញ​ពី​ឆ្វេង ឬ​​គ្រាប់​ចុច​​និមិត្ត​សញ្ញា"</string>
-    <string name="key_preview_popup_dismiss_delay" msgid="6213164897443068248">"​សោ​លេចឡើង​បោះបង់​ការ​​ពន្យារពេល​"</string>
+    <string name="key_preview_popup_dismiss_delay" msgid="6213164897443068248">"​សោ​លេចឡើង​បោះបង់​ការ​​ពន្យារពេល"</string>
     <string name="key_preview_popup_dismiss_no_delay" msgid="2096123151571458064">"គ្មាន​ការ​ពន្យារពេល"</string>
     <string name="key_preview_popup_dismiss_default_delay" msgid="2166964333903906734">"លំនាំដើម"</string>
     <string name="abbreviation_unit_milliseconds" msgid="8700286094028323363">"<xliff:g id="MILLISECONDS">%s</xliff:g> មិល្លី​វិនាទី"</string>
@@ -49,7 +49,7 @@
     <string name="use_personalized_dicts" msgid="5167396352105467626">"ការ​ស្នើ​ផ្ទាល់​ខ្លួន"</string>
     <string name="use_double_space_period" msgid="8781529969425082860">"រយៈ​ពេល​ចុច​ដកឃ្លា​ពីរដង"</string>
     <string name="use_double_space_period_summary" msgid="6532892187247952799">"ប៉ះ​ដកឃ្លា​ពីរ​​ដង​បញ្ចូល​​​រយៈ​ពេល​ដែល​អនុវត្ត​តាម​ដកឃ្លា"</string>
-    <string name="auto_cap" msgid="1719746674854628252">"ការ​សរសេរ​ជា​អក្សរ​ធំ​​ស្វ័យប្រវត្តិ​"</string>
+    <string name="auto_cap" msgid="1719746674854628252">"ការ​សរសេរ​ជា​អក្សរ​ធំ​​ស្វ័យប្រវត្តិ"</string>
     <string name="auto_cap_summary" msgid="7934452761022946874">"សរសេរ​ពាក្យ​ដំបូង​​​ជា​អក្សរ​ធំ​​នៃ​ប្រយោគ​នីមួយ​ៗ"</string>
     <string name="edit_personal_dictionary" msgid="3996910038952940420">"វចនានុក្រម​ផ្ទាល់ខ្លួន"</string>
     <string name="configure_dictionaries_title" msgid="4238652338556902049">"ផ្នែក​បន្ថែម​វចនានុក្រម"</string>
@@ -60,7 +60,7 @@
     <string name="prefs_suggestion_visibility_show_only_portrait_name" msgid="3859783767435239118">"បង្ហាញ​នៅ​ក្នុង​របៀប​បញ្ឈរ"</string>
     <string name="prefs_suggestion_visibility_hide_name" msgid="6309143926422234673">"លាក់​ជានិច្ច"</string>
     <string name="prefs_block_potentially_offensive_title" msgid="5078480071057408934">"ទប់ស្កាត់​​ពាក្យ​​បំពាន"</string>
-    <string name="prefs_block_potentially_offensive_summary" msgid="2371835479734991364">"កុំ​ស្នើ​ឲ្យ​ពាក្យ​បំពាន​មាន​សក្ដានុពល​"</string>
+    <string name="prefs_block_potentially_offensive_summary" msgid="2371835479734991364">"កុំ​ស្នើ​ឲ្យ​ពាក្យ​បំពាន​មាន​សក្ដានុពល"</string>
     <string name="auto_correction" msgid="7630720885194996950">"ការ​កែ​​​ស្វ័យប្រវត្តិ"</string>
     <string name="auto_correction_summary" msgid="5625751551134658006">"ចន្លោះ​មិន​ឃើញ ​និង​សញ្ញា​​វណ្ណយុត្ត​កែ​ពាក្យ​ដែល​បាន​វាយ​ខុស​ស្វ័យប្រវត្តិ"</string>
     <string name="auto_correction_threshold_mode_off" msgid="8470882665417944026">"បិទ"</string>
@@ -123,7 +123,7 @@
     <string name="prefs_keypress_vibration_duration_settings" msgid="7918341459947439226">"ថិរវេលា​​ញ័រ​​ពេល​ចុច​គ្រាប់ចុច"</string>
     <string name="prefs_keypress_sound_volume_settings" msgid="6027007337036891623">"កម្រិត​សំឡេង​ពេល​ចុច​គ្រាប់​ចុច"</string>
     <string name="prefs_read_external_dictionary" msgid="2588931418575013067">"អាន​ឯកសារ​វចនានុក្រម​ខាង​ក្រៅ"</string>
-    <string name="read_external_dictionary_no_files_message" msgid="4947420942224623792">"គ្មាន​ឯកសារ​វចនានុក្រម​នៅ​ក្នុង​ថត​ទាញ​យក​​"</string>
+    <string name="read_external_dictionary_no_files_message" msgid="4947420942224623792">"គ្មាន​ឯកសារ​វចនានុក្រម​នៅ​ក្នុង​ថត​ទាញ​យក"</string>
     <string name="read_external_dictionary_multiple_files_title" msgid="7637749044265808628">"ជ្រើស​ឯកសារ​វចនានុក្រម​ ដើម្បី​ដំឡើង"</string>
     <string name="read_external_dictionary_confirm_install_message" msgid="4782116251651288054">"ពិត​ជា​ដំឡើង​ឯកសារ​នេះ​សម្រាប់ <xliff:g id="LANGUAGE_NAME">%s</xliff:g>?"</string>
     <string name="error" msgid="8940763624668513648">"មាន​កំហុស"</string>
@@ -154,7 +154,7 @@
     <string name="dictionary_provider_name" msgid="3027315045397363079">"កម្មវិធី​ផ្ដល់​វចនានុក្រម"</string>
     <string name="dictionary_service_name" msgid="6237472350693511448">"សេវាកម្ម​​វចនានុក្រម"</string>
     <string name="download_description" msgid="6014835283119198591">"ព័ត៌មាន​បច្ចុប្បន្នភាព​វចនានុក្រម"</string>
-    <string name="dictionary_settings_title" msgid="8091417676045693313">"ផ្នែក​បន្ថែម​វចនានុក្រម​​"</string>
+    <string name="dictionary_settings_title" msgid="8091417676045693313">"ផ្នែក​បន្ថែម​វចនានុក្រម"</string>
     <string name="dictionary_install_over_metered_network_prompt" msgid="3587517870006332980">"វចនានុក្រម​​​​​អាច​ប្រើ​បាន"</string>
     <string name="dictionary_settings_summary" msgid="5305694987799824349">"ការ​កំណត់​សម្រាប់​វចនានុក្រម"</string>
     <string name="user_dictionaries" msgid="3582332055892252845">"វចនានុក្រម​​​អ្នក​ប្រើ"</string>
@@ -170,10 +170,10 @@
     <string name="message_updating" msgid="4457761393932375219">"ពិនិត្យមើល​បច្ចុប្បន្នភាព"</string>
     <string name="message_loading" msgid="5638680861387748936">"កំពុង​ផ្ទុក..."</string>
     <string name="main_dict_description" msgid="3072821352793492143">"វចនានុក្រម​ចម្បង"</string>
-    <string name="cancel" msgid="6830980399865683324">"បោះ​បង់​"</string>
+    <string name="cancel" msgid="6830980399865683324">"បោះ​បង់"</string>
     <string name="go_to_settings" msgid="3876892339342569259">"ការ​កំណត់"</string>
     <string name="install_dict" msgid="180852772562189365">"ដំឡើង"</string>
-    <string name="cancel_download_dict" msgid="7843340278507019303">"បោះ​បង់​"</string>
+    <string name="cancel_download_dict" msgid="7843340278507019303">"បោះ​បង់"</string>
     <string name="delete_dict" msgid="756853268088330054">"លុប"</string>
     <string name="should_download_over_metered_prompt" msgid="1583881200688185508">"ភាសា​ដែល​បាន​ជ្រើស​នៅ​លើ​ឧបករណ៍​ចល័ត​មាន​វចនានុក្រម​អាច​ប្រើ​បាន។&lt;br/&gt; យើង​ផ្ដល់​អនុសាសន៍​ឲ្យ &lt;b&gt;ទាញ​យក&lt;/b&gt; វចនានុក្រម​ភាសា <xliff:g id="LANGUAGE_NAME">%1$s</xliff:g> ដើម្បី​បង្កើន​បទពិសោធន៍​វាយ​បញ្ចូល​របស់​អ្នក។&lt;br/&gt; &lt;br/&gt; ការ​ទាញ​យក​អាច​ចំណាយ​ពេល​ប្រហែល​ពីរ​នាទី​នៅ​តាម 3G។ ការ​គិត​ថ្លៃ​អាច​អនុវត្ត​ប្រសិន​បើ​អ្នក​មិន​ប្រើ &lt;b&gt;ផែនការ​ទិន្នន័យ​គ្មាន​ដែន​កំណត់&lt;/b&gt;.&lt;br/&gt; បើ​អ្នក​មិន​ប្រាកដ​​ថា​ផែនការ​ណា​មួយ​ដែល​អ្នក​មាន យើង​ផ្ដល់​អនុសាសន៍​ឲ្យ​​ភ្ជាប់​វ៉ាយហ្វាយ ដើម្បី​ចាប់ផ្ដើម​ទាញ​យក​ដោយ​ស្វ័យ​ប្រវត្តិ។&lt;br/&gt; &lt;br/&gt; ជំនួយ៖ អ្នក​អាច​ទាញ​យក និង​លុប​វចនានុក្រម​ដោយ​ចូល​ទៅ​ &lt;b&gt;ភាសា &amp; ការ​បញ្ចូល&lt;/b&gt; នៅ​ក្នុង​ម៉ឺនុយ &lt;b&gt;ការ​កំណត់&lt;/b&gt; សម្រាប់​ឧបករណ៍​ចល័ត។"</string>
     <string name="download_over_metered" msgid="1643065851159409546">"ទាញ​យក​ឥឡូវ​នេះ (<xliff:g id="SIZE_IN_MEGABYTES">%1$.1f</xliff:g> មេកាបៃ)"</string>
@@ -191,7 +191,7 @@
     <string name="user_dict_settings_add_word_option_name" msgid="6665558053408962865">"ពាក្យ៖"</string>
     <string name="user_dict_settings_add_shortcut_option_name" msgid="3094731590655523777">"ផ្លូវកាត់​៖"</string>
     <string name="user_dict_settings_add_locale_option_name" msgid="4738643440987277705">"ភាសា៖"</string>
-    <string name="user_dict_settings_add_word_hint" msgid="4902434148985906707">"វាយ​បញ្ចូល​ពាក្យ​"</string>
+    <string name="user_dict_settings_add_word_hint" msgid="4902434148985906707">"វាយ​បញ្ចូល​ពាក្យ"</string>
     <string name="user_dict_settings_add_shortcut_hint" msgid="2265453012555060178">"ផ្លូវកាត់​ជា​ជម្រើស"</string>
     <string name="user_dict_settings_edit_dialog_title" msgid="3765774633869590352">"កែ​ពាក្យ"</string>
     <string name="user_dict_settings_context_menu_edit_title" msgid="6812255903472456302">"កែ"</string>
diff --git a/java/src/com/android/inputmethod/keyboard/internal/KeyboardTextsTable.java b/java/src/com/android/inputmethod/keyboard/internal/KeyboardTextsTable.java
index 1a27be9..7e6181a 100644
--- a/java/src/com/android/inputmethod/keyboard/internal/KeyboardTextsTable.java
+++ b/java/src/com/android/inputmethod/keyboard/internal/KeyboardTextsTable.java
@@ -3588,33 +3588,33 @@
         // U+00E5: "å" LATIN SMALL LETTER A WITH RING ABOVE
         // U+0101: "ā" LATIN SMALL LETTER A WITH MACRON
         /* morekeys_a */ "\u00E0,\u00E1,\u00E2,\u00E4,\u00E6,\u00E3,\u00E5,\u0101",
+        // U+00F3: "ó" LATIN SMALL LETTER O WITH ACUTE
         // U+00F4: "ô" LATIN SMALL LETTER O WITH CIRCUMFLEX
         // U+00F6: "ö" LATIN SMALL LETTER O WITH DIAERESIS
         // U+00F2: "ò" LATIN SMALL LETTER O WITH GRAVE
-        // U+00F3: "ó" LATIN SMALL LETTER O WITH ACUTE
         // U+0153: "œ" LATIN SMALL LIGATURE OE
         // U+00F8: "ø" LATIN SMALL LETTER O WITH STROKE
         // U+014D: "ō" LATIN SMALL LETTER O WITH MACRON
         // U+00F5: "õ" LATIN SMALL LETTER O WITH TILDE
-        /* morekeys_o */ "\u00F4,\u00F6,\u00F2,\u00F3,\u0153,\u00F8,\u014D,\u00F5",
+        /* morekeys_o */ "\u00F3,\u00F4,\u00F6,\u00F2,\u0153,\u00F8,\u014D,\u00F5",
+        // U+00FA: "ú" LATIN SMALL LETTER U WITH ACUTE
         // U+00FB: "û" LATIN SMALL LETTER U WITH CIRCUMFLEX
         // U+00FC: "ü" LATIN SMALL LETTER U WITH DIAERESIS
         // U+00F9: "ù" LATIN SMALL LETTER U WITH GRAVE
-        // U+00FA: "ú" LATIN SMALL LETTER U WITH ACUTE
         // U+016B: "ū" LATIN SMALL LETTER U WITH MACRON
-        /* morekeys_u */ "\u00FB,\u00FC,\u00F9,\u00FA,\u016B",
-        // U+00E8: "è" LATIN SMALL LETTER E WITH GRAVE
+        /* morekeys_u */ "\u00FA,\u00FB,\u00FC,\u00F9,\u016B",
         // U+00E9: "é" LATIN SMALL LETTER E WITH ACUTE
+        // U+00E8: "è" LATIN SMALL LETTER E WITH GRAVE
         // U+00EA: "ê" LATIN SMALL LETTER E WITH CIRCUMFLEX
         // U+00EB: "ë" LATIN SMALL LETTER E WITH DIAERESIS
         // U+0113: "ē" LATIN SMALL LETTER E WITH MACRON
-        /* morekeys_e */ "\u00E8,\u00E9,\u00EA,\u00EB,\u0113",
+        /* morekeys_e */ "\u00E9,\u00E8,\u00EA,\u00EB,\u0113",
+        // U+00ED: "í" LATIN SMALL LETTER I WITH ACUTE
         // U+00EE: "î" LATIN SMALL LETTER I WITH CIRCUMFLEX
         // U+00EF: "ï" LATIN SMALL LETTER I WITH DIAERESIS
-        // U+00ED: "í" LATIN SMALL LETTER I WITH ACUTE
         // U+012B: "ī" LATIN SMALL LETTER I WITH MACRON
         // U+00EC: "ì" LATIN SMALL LETTER I WITH GRAVE
-        /* morekeys_i */ "\u00EE,\u00EF,\u00ED,\u012B,\u00EC",
+        /* morekeys_i */ "\u00ED,\u00EE,\u00EF,\u012B,\u00EC",
         // U+00E7: "ç" LATIN SMALL LETTER C WITH CEDILLA
         /* morekeys_c */ "\u00E7",
         /* double_quotes */ null,
diff --git a/java/src/com/android/inputmethod/latin/BinaryDictionary.java b/java/src/com/android/inputmethod/latin/BinaryDictionary.java
index 83ee982..94a1e36 100644
--- a/java/src/com/android/inputmethod/latin/BinaryDictionary.java
+++ b/java/src/com/android/inputmethod/latin/BinaryDictionary.java
@@ -373,8 +373,7 @@
         return getProbabilityNative(mNativeDict, codePoints);
     }
 
-    // TODO: Add a batch process version (isValidBigramMultiple?) to avoid excessive numbers of jni
-    // calls when checking for changes in an entire dictionary.
+    @UsedForTesting
     public boolean isValidBigram(final String word0, final String word1) {
         return getBigramProbability(word0, word1) != NOT_A_PROBABILITY;
     }
@@ -541,7 +540,9 @@
         close();
         final File dictFile = new File(mDictFilePath);
         final File tmpDictFile = new File(tmpDictFilePath);
-        FileUtils.deleteRecursively(dictFile);
+        if (!FileUtils.deleteRecursively(dictFile)) {
+            return false;
+        }
         if (!BinaryDictionaryUtils.renameDict(tmpDictFile, dictFile)) {
             return false;
         }
diff --git a/java/src/com/android/inputmethod/latin/ContactsBinaryDictionary.java b/java/src/com/android/inputmethod/latin/ContactsBinaryDictionary.java
index 9bc01a2..e04fcda 100644
--- a/java/src/com/android/inputmethod/latin/ContactsBinaryDictionary.java
+++ b/java/src/com/android/inputmethod/latin/ContactsBinaryDictionary.java
@@ -31,9 +31,12 @@
 
 import com.android.inputmethod.annotations.UsedForTesting;
 import com.android.inputmethod.latin.personalization.AccountUtils;
+import com.android.inputmethod.latin.utils.CollectionUtils;
+import com.android.inputmethod.latin.utils.ExecutorUtils;
 import com.android.inputmethod.latin.utils.StringUtils;
 
 import java.io.File;
+import java.util.ArrayList;
 import java.util.List;
 import java.util.Locale;
 
@@ -60,7 +63,10 @@
     private static final int INDEX_NAME = 1;
 
     /** The number of contacts in the most recent dictionary rebuild. */
-    static private int sContactCountAtLastRebuild = 0;
+    private int mContactCountAtLastRebuild = 0;
+
+    /** The hash code of ArrayList of contacts names in the most recent dictionary rebuild. */
+    private int mHashCodeAtLastRebuild = 0;
 
     private ContentObserver mObserver;
 
@@ -96,7 +102,14 @@
                 new ContentObserver(null) {
                     @Override
                     public void onChange(boolean self) {
-                        setNeedsToReload();
+                        ExecutorUtils.getExecutor("Check Contacts").execute(new Runnable() {
+                            @Override
+                            public void run() {
+                                if (haveContentsChanged()) {
+                                    setNeedsToRecreate();
+                                }
+                            }
+                        });
                     }
                 });
     }
@@ -143,7 +156,7 @@
                 return;
             }
             if (cursor.moveToFirst()) {
-                sContactCountAtLastRebuild = getContactCount();
+                mContactCountAtLastRebuild = getContactCount();
                 addWordsLocked(cursor);
             }
         } catch (final SQLiteException e) {
@@ -167,9 +180,11 @@
 
     private void addWordsLocked(final Cursor cursor) {
         int count = 0;
+        final ArrayList<String> names = CollectionUtils.newArrayList();
         while (!cursor.isAfterLast() && count < MAX_CONTACT_COUNT) {
             String name = cursor.getString(INDEX_NAME);
             if (isValidName(name)) {
+                names.add(name);
                 addNameLocked(name);
                 ++count;
             } else {
@@ -179,6 +194,7 @@
             }
             cursor.moveToNext();
         }
+        mHashCodeAtLastRebuild = names.hashCode();
     }
 
     private int getContactCount() {
@@ -258,8 +274,7 @@
         return end;
     }
 
-    @Override
-    protected boolean haveContentsChanged() {
+    private boolean haveContentsChanged() {
         final long startTime = SystemClock.uptimeMillis();
         final int contactCount = getContactCount();
         if (contactCount > MAX_CONTACT_COUNT) {
@@ -268,9 +283,9 @@
             // TODO: Sort and check only the MAX_CONTACT_COUNT most recent contacts?
             return false;
         }
-        if (contactCount != sContactCountAtLastRebuild) {
+        if (contactCount != mContactCountAtLastRebuild) {
             if (DEBUG) {
-                Log.d(TAG, "Contact count changed: " + sContactCountAtLastRebuild + " to "
+                Log.d(TAG, "Contact count changed: " + mContactCountAtLastRebuild + " to "
                         + contactCount);
             }
             return true;
@@ -283,20 +298,20 @@
         if (null == cursor) {
             return false;
         }
+        final ArrayList<String> names = CollectionUtils.newArrayList();
         try {
             if (cursor.moveToFirst()) {
                 while (!cursor.isAfterLast()) {
                     String name = cursor.getString(INDEX_NAME);
-                    if (isValidName(name) && !isNameInDictionaryLocked(name)) {
-                        if (DEBUG) {
-                            Log.d(TAG, "Contact name missing: " + name + " (runtime = "
-                                    + (SystemClock.uptimeMillis() - startTime) + " ms)");
-                        }
-                        return true;
+                    if (isValidName(name)) {
+                        names.add(name);
                     }
                     cursor.moveToNext();
                 }
             }
+            if (names.hashCode() != mHashCodeAtLastRebuild) {
+                return true;
+            }
         } finally {
             cursor.close();
         }
@@ -313,33 +328,4 @@
         }
         return false;
     }
-
-    /**
-     * Checks if the words in a name are in the current binary dictionary.
-     */
-    private boolean isNameInDictionaryLocked(final String name) {
-        int len = StringUtils.codePointCount(name);
-        String prevWord = null;
-        for (int i = 0; i < len; i++) {
-            if (Character.isLetter(name.codePointAt(i))) {
-                int end = getWordEndPosition(name, len, i);
-                String word = name.substring(i, end);
-                i = end - 1;
-                final int wordLen = StringUtils.codePointCount(word);
-                if (wordLen < MAX_WORD_LENGTH && wordLen > 1) {
-                    if (!TextUtils.isEmpty(prevWord) && mUseFirstLastBigrams) {
-                        if (!isValidBigramLocked(prevWord, word)) {
-                            return false;
-                        }
-                    } else {
-                        if (!isValidWordLocked(word)) {
-                            return false;
-                        }
-                    }
-                    prevWord = word;
-                }
-            }
-        }
-        return true;
-    }
 }
diff --git a/java/src/com/android/inputmethod/latin/ExpandableBinaryDictionary.java b/java/src/com/android/inputmethod/latin/ExpandableBinaryDictionary.java
index e3bed31..6818c15 100644
--- a/java/src/com/android/inputmethod/latin/ExpandableBinaryDictionary.java
+++ b/java/src/com/android/inputmethod/latin/ExpandableBinaryDictionary.java
@@ -92,8 +92,8 @@
     /** Indicates whether a task for reloading the dictionary has been scheduled. */
     private final AtomicBoolean mIsReloading;
 
-    /** Indicates whether the current dictionary needs to be reloaded. */
-    private boolean mNeedsToReload;
+    /** Indicates whether the current dictionary needs to be recreated. */
+    private boolean mNeedsToRecreate;
 
     private final ReentrantReadWriteLock mLock;
 
@@ -107,20 +107,14 @@
      */
     protected abstract void loadInitialContentsLocked();
 
-    /**
-     * Indicates that the source dictionary contents have changed and a rebuild of the binary file
-     * is required. If it returns false, the next reload will only read the current binary
-     * dictionary from file.
-     */
-    protected abstract boolean haveContentsChanged();
-
     private boolean matchesExpectedBinaryDictFormatVersionForThisType(final int formatVersion) {
         return formatVersion == FormatSpec.VERSION4;
     }
 
     private boolean needsToMigrateDictionary(final int formatVersion) {
-        // TODO: Check version.
-        return false;
+        // When we bump up the dictionary format version, the old version should be added to here
+        // for supporting migration. Note that native code has to support reading such formats.
+        return formatVersion == FormatSpec.VERSION4_ONLY_FOR_TESTING;
     }
 
     public boolean isValidDictionaryLocked() {
@@ -147,7 +141,7 @@
         mDictFile = getDictFile(context, dictName, dictFile);
         mBinaryDictionary = null;
         mIsReloading = new AtomicBoolean();
-        mNeedsToReload = false;
+        mNeedsToRecreate = false;
         mLock = new ReentrantReadWriteLock();
     }
 
@@ -489,11 +483,11 @@
     }
 
     /**
-     * Marks that the dictionary needs to be reloaded.
+     * Marks that the dictionary needs to be recreated.
      *
      */
-    protected void setNeedsToReload() {
-        mNeedsToReload = true;
+    protected void setNeedsToRecreate() {
+        mNeedsToRecreate = true;
     }
 
     /**
@@ -511,7 +505,7 @@
      * Returns whether a dictionary reload is required.
      */
     private boolean isReloadRequired() {
-        return mBinaryDictionary == null || mNeedsToReload;
+        return mBinaryDictionary == null || mNeedsToRecreate;
     }
 
     /**
@@ -523,8 +517,7 @@
                 @Override
                 public void run() {
                     try {
-                        // TODO: Quit checking contents in ExpandableBinaryDictionary.
-                        if (!mDictFile.exists() || (mNeedsToReload && haveContentsChanged())) {
+                        if (!mDictFile.exists() || mNeedsToRecreate) {
                             // If the dictionary file does not exist or contents have been updated,
                             // generate a new one.
                             createNewDictionaryLocked();
@@ -536,12 +529,12 @@
                                     && matchesExpectedBinaryDictFormatVersionForThisType(
                                             mBinaryDictionary.getFormatVersion()))) {
                                 // Binary dictionary or its format version is not valid. Regenerate
-                                // the dictionary file. writeBinaryDictionary will remove the
+                                // the dictionary file. createNewDictionaryLocked will remove the
                                 // existing files if appropriate.
                                 createNewDictionaryLocked();
                             }
                         }
-                        mNeedsToReload = false;
+                        mNeedsToRecreate = false;
                     } finally {
                         mIsReloading.set(false);
                     }
diff --git a/java/src/com/android/inputmethod/latin/UserBinaryDictionary.java b/java/src/com/android/inputmethod/latin/UserBinaryDictionary.java
index e1cda69..c8ffbe4 100644
--- a/java/src/com/android/inputmethod/latin/UserBinaryDictionary.java
+++ b/java/src/com/android/inputmethod/latin/UserBinaryDictionary.java
@@ -98,7 +98,7 @@
             // devices. On older versions of the platform, the hook above will be called instead.
             @Override
             public void onChange(final boolean self, final Uri uri) {
-                setNeedsToReload();
+                setNeedsToRecreate();
             }
         };
         cres.registerContentObserver(Words.CONTENT_URI, true, mObserver);
@@ -272,9 +272,4 @@
             }
         }
     }
-
-    @Override
-    protected boolean haveContentsChanged() {
-        return true;
-    }
 }
diff --git a/java/src/com/android/inputmethod/latin/makedict/FormatSpec.java b/java/src/com/android/inputmethod/latin/makedict/FormatSpec.java
index f255034..613ff2b 100644
--- a/java/src/com/android/inputmethod/latin/makedict/FormatSpec.java
+++ b/java/src/com/android/inputmethod/latin/makedict/FormatSpec.java
@@ -186,7 +186,12 @@
     // From version 4 on, we use version * 100 + revision as a version number. That allows
     // us to change the format during development while having testing devices remove
     // older files with each upgrade, while still having a readable versioning scheme.
+    // When we bump up the dictionary format version, we should update
+    // ExpandableDictionary.needsToMigrateDictionary() and
+    // ExpandableDictionary.matchesExpectedBinaryDictFormatVersionForThisType().
     public static final int VERSION2 = 2;
+    // Dictionary version used for testing.
+    public static final int VERSION4_ONLY_FOR_TESTING = 399;
     public static final int VERSION4 = 401;
     static final int MINIMUM_SUPPORTED_VERSION = VERSION2;
     static final int MAXIMUM_SUPPORTED_VERSION = VERSION4;
diff --git a/java/src/com/android/inputmethod/latin/personalization/DecayingExpandableBinaryDictionaryBase.java b/java/src/com/android/inputmethod/latin/personalization/DecayingExpandableBinaryDictionaryBase.java
index 38c28a7..06bdba0 100644
--- a/java/src/com/android/inputmethod/latin/personalization/DecayingExpandableBinaryDictionaryBase.java
+++ b/java/src/com/android/inputmethod/latin/personalization/DecayingExpandableBinaryDictionaryBase.java
@@ -74,11 +74,6 @@
     }
 
     @Override
-    protected boolean haveContentsChanged() {
-        return false;
-    }
-
-    @Override
     protected void loadInitialContentsLocked() {
         // No initial contents.
     }
diff --git a/java/src/com/android/inputmethod/latin/personalization/DictionaryDecayBroadcastReciever.java b/java/src/com/android/inputmethod/latin/personalization/DictionaryDecayBroadcastReciever.java
index de2744f..221bb9a 100644
--- a/java/src/com/android/inputmethod/latin/personalization/DictionaryDecayBroadcastReciever.java
+++ b/java/src/com/android/inputmethod/latin/personalization/DictionaryDecayBroadcastReciever.java
@@ -61,6 +61,7 @@
         final String action = intent.getAction();
         if (action.equals(DICTIONARY_DECAY_INTENT_ACTION)) {
             PersonalizationHelper.runGCOnAllOpenedUserHistoryDictionaries();
+            PersonalizationHelper.runGCOnAllOpenedPersonalizationDictionaries();
         }
     }
 }
diff --git a/java/src/com/android/inputmethod/latin/personalization/PersonalizationHelper.java b/java/src/com/android/inputmethod/latin/personalization/PersonalizationHelper.java
index 7c43182..afacd08 100644
--- a/java/src/com/android/inputmethod/latin/personalization/PersonalizationHelper.java
+++ b/java/src/com/android/inputmethod/latin/personalization/PersonalizationHelper.java
@@ -16,7 +16,6 @@
 
 package com.android.inputmethod.latin.personalization;
 
-import com.android.inputmethod.annotations.UsedForTesting;
 import com.android.inputmethod.latin.utils.CollectionUtils;
 import com.android.inputmethod.latin.utils.FileUtils;
 
@@ -66,8 +65,8 @@
         if (TimeUnit.MILLISECONDS.toSeconds(
                 DictionaryDecayBroadcastReciever.DICTIONARY_DECAY_INTERVAL)
                         < currentTimestamp - sCurrentTimestampForTesting) {
-            // TODO: Run GC for both PersonalizationDictionary and UserHistoryDictionary.
             runGCOnAllOpenedUserHistoryDictionaries();
+            runGCOnAllOpenedPersonalizationDictionaries();
         }
     }
 
@@ -75,7 +74,6 @@
         runGCOnAllDictionariesIfRequired(sLangUserHistoryDictCache);
     }
 
-    @UsedForTesting
     public static void runGCOnAllOpenedPersonalizationDictionaries() {
         runGCOnAllDictionariesIfRequired(sLangPersonalizationDictCache);
     }
diff --git a/native/jni/src/suggest/policyimpl/dictionary/bigram/ver4_bigram_list_policy.cpp b/native/jni/src/suggest/policyimpl/dictionary/bigram/ver4_bigram_list_policy.cpp
index 04e768f..4975512 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/bigram/ver4_bigram_list_policy.cpp
+++ b/native/jni/src/suggest/policyimpl/dictionary/bigram/ver4_bigram_list_policy.cpp
@@ -50,12 +50,18 @@
 
 bool Ver4BigramListPolicy::addNewEntry(const int terminalId, const int newTargetTerminalId,
         const int newProbability, const int timestamp, bool *const outAddedNewEntry) {
+    // 1. The word has no bigrams yet.
+    // 2. The word has bigrams, and there is the target in the list.
+    // 3. The word has bigrams, and there is an invalid entry that can be reclaimed.
+    // 4. The word has bigrams. We have to append new bigram entry to the list.
+    // 5. Same as 4, but the list is the last entry of the content file.
+
     if (outAddedNewEntry) {
         *outAddedNewEntry = false;
     }
     const int bigramListPos = mBigramDictContent->getBigramListHeadPos(terminalId);
     if (bigramListPos == NOT_A_DICT_POS) {
-        // Updating PtNode that doesn't have a bigram list.
+        // Case 1. PtNode that doesn't have a bigram list.
         // Create new bigram list.
         if (!mBigramDictContent->createNewBigramList(terminalId)) {
             return false;
@@ -75,50 +81,55 @@
         return true;
     }
 
-    const int entryPosToUpdate = getEntryPosToUpdate(newTargetTerminalId, bigramListPos);
-    if (entryPosToUpdate != NOT_A_DICT_POS) {
-        // Overwrite existing entry.
-        const BigramEntry originalBigramEntry =
-                mBigramDictContent->getBigramEntry(entryPosToUpdate);
-        if (!originalBigramEntry.isValid()) {
-            // Reuse invalid entry.
-            if (outAddedNewEntry) {
-                *outAddedNewEntry = true;
+    int tailEntryPos = NOT_A_DICT_POS;
+    const int entryPosToUpdate = getEntryPosToUpdate(newTargetTerminalId, bigramListPos,
+            &tailEntryPos);
+    if (tailEntryPos != NOT_A_DICT_POS || entryPosToUpdate == NOT_A_DICT_POS) {
+        // Case 4, 5.
+        // Add new entry to the bigram list.
+        if (tailEntryPos == NOT_A_DICT_POS) {
+            // Case 4. Create new bigram list.
+            if (!mBigramDictContent->createNewBigramList(terminalId)) {
+                return false;
+            }
+            const int destPos = mBigramDictContent->getBigramListHeadPos(terminalId);
+            // Copy existing bigram list.
+            if (!mBigramDictContent->copyBigramList(bigramListPos, destPos, &tailEntryPos)) {
+                return false;
             }
         }
-        const BigramEntry updatedBigramEntry =
-                originalBigramEntry.updateTargetTerminalIdAndGetEntry(newTargetTerminalId);
+        // Write new entry at the tail position of the bigram content.
+        const BigramEntry newBigramEntry(false /* hasNext */, NOT_A_PROBABILITY,
+                newTargetTerminalId);
         const BigramEntry bigramEntryToWrite = createUpdatedBigramEntryFrom(
-                &updatedBigramEntry, newProbability, timestamp);
-        return mBigramDictContent->writeBigramEntry(&bigramEntryToWrite, entryPosToUpdate);
+                &newBigramEntry, newProbability, timestamp);
+        if (!mBigramDictContent->writeBigramEntryAtTail(&bigramEntryToWrite)) {
+            return false;
+        }
+        // Update has next flag of the tail entry.
+        if (!updateHasNextFlag(true /* hasNext */, tailEntryPos)) {
+            return false;
+        }
+        if (outAddedNewEntry) {
+            *outAddedNewEntry = true;
+        }
+        return true;
     }
 
-    // Add new entry to the bigram list.
-    // Create new bigram list.
-    if (!mBigramDictContent->createNewBigramList(terminalId)) {
-        return false;
+    // Case 2. Overwrite the existing entry. Case 3. Reclaim and reuse the existing invalid entry.
+    const BigramEntry originalBigramEntry = mBigramDictContent->getBigramEntry(entryPosToUpdate);
+    if (!originalBigramEntry.isValid()) {
+        // Case 3. Reuse the existing invalid entry. outAddedNewEntry is false when an existing
+        // entry is updated.
+        if (outAddedNewEntry) {
+            *outAddedNewEntry = true;
+        }
     }
-    int writingPos = mBigramDictContent->getBigramListHeadPos(terminalId);
-    int tailEntryPos = NOT_A_DICT_POS;
-    // Copy existing bigram list.
-    if (!mBigramDictContent->copyBigramList(bigramListPos, writingPos, &tailEntryPos)) {
-        return false;
-    }
-    // Write new entry at the tail position of the bigram content.
-    const BigramEntry newBigramEntry(false /* hasNext */, NOT_A_PROBABILITY, newTargetTerminalId);
+    const BigramEntry updatedBigramEntry =
+            originalBigramEntry.updateTargetTerminalIdAndGetEntry(newTargetTerminalId);
     const BigramEntry bigramEntryToWrite = createUpdatedBigramEntryFrom(
-            &newBigramEntry, newProbability, timestamp);
-    if (!mBigramDictContent->writeBigramEntryAtTail(&bigramEntryToWrite)) {
-        return false;
-    }
-    // Update has next flag of the tail entry.
-    if (!updateHasNextFlag(true /* hasNext */, tailEntryPos)) {
-        return false;
-    }
-    if (outAddedNewEntry) {
-        *outAddedNewEntry = true;
-    }
-    return true;
+            &updatedBigramEntry, newProbability, timestamp);
+    return mBigramDictContent->writeBigramEntry(&bigramEntryToWrite, entryPosToUpdate);
 }
 
 bool Ver4BigramListPolicy::removeEntry(const int terminalId, const int targetTerminalId) {
@@ -127,7 +138,8 @@
         // Bigram list doesn't exist.
         return false;
     }
-    const int entryPosToUpdate = getEntryPosToUpdate(targetTerminalId, bigramListPos);
+    const int entryPosToUpdate = getEntryPosToUpdate(targetTerminalId, bigramListPos,
+            nullptr /* outTailEntryPos */);
     if (entryPosToUpdate == NOT_A_DICT_POS) {
         // Bigram entry doesn't exist.
         return false;
@@ -212,7 +224,10 @@
 }
 
 int Ver4BigramListPolicy::getEntryPosToUpdate(const int targetTerminalIdToFind,
-        const int bigramListPos) const {
+        const int bigramListPos, int *const outTailEntryPos) const {
+    if (outTailEntryPos) {
+        *outTailEntryPos = NOT_A_DICT_POS;
+    }
     bool hasNext = true;
     int invalidEntryPos = NOT_A_DICT_POS;
     int readingPos = bigramListPos;
@@ -228,6 +243,11 @@
             // Invalid entry that can be reused is found.
             invalidEntryPos = entryPos;
         }
+        if (!hasNext && mBigramDictContent->isContentTailPos(readingPos)) {
+            if (outTailEntryPos) {
+                *outTailEntryPos = entryPos;
+            }
+        }
     }
     return invalidEntryPos;
 }
diff --git a/native/jni/src/suggest/policyimpl/dictionary/bigram/ver4_bigram_list_policy.h b/native/jni/src/suggest/policyimpl/dictionary/bigram/ver4_bigram_list_policy.h
index d8f7be6..c1f3335 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/bigram/ver4_bigram_list_policy.h
+++ b/native/jni/src/suggest/policyimpl/dictionary/bigram/ver4_bigram_list_policy.h
@@ -56,7 +56,8 @@
  private:
     DISALLOW_IMPLICIT_CONSTRUCTORS(Ver4BigramListPolicy);
 
-    int getEntryPosToUpdate(const int targetTerminalIdToFind, const int bigramListPos) const;
+    int getEntryPosToUpdate(const int targetTerminalIdToFind, const int bigramListPos,
+            int *const outTailEntryPos) const;
 
     const BigramEntry createUpdatedBigramEntryFrom(const BigramEntry *const originalBigramEntry,
             const int newProbability, const int timestamp) const;
diff --git a/native/jni/src/suggest/policyimpl/dictionary/header/header_policy.h b/native/jni/src/suggest/policyimpl/dictionary/header/header_policy.h
index e4a6dc5..da24302 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/header/header_policy.h
+++ b/native/jni/src/suggest/policyimpl/dictionary/header/header_policy.h
@@ -139,6 +139,8 @@
         switch (mDictFormatVersion) {
             case FormatUtils::VERSION_2:
                 return FormatUtils::VERSION_2;
+            case FormatUtils::VERSION_4_ONLY_FOR_TESTING:
+                return FormatUtils::VERSION_4_ONLY_FOR_TESTING;
             case FormatUtils::VERSION_4:
                 return FormatUtils::VERSION_4;
             default:
diff --git a/native/jni/src/suggest/policyimpl/dictionary/header/header_read_write_utils.cpp b/native/jni/src/suggest/policyimpl/dictionary/header/header_read_write_utils.cpp
index 5608e27..2a9028a 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/header/header_read_write_utils.cpp
+++ b/native/jni/src/suggest/policyimpl/dictionary/header/header_read_write_utils.cpp
@@ -98,8 +98,9 @@
         case FormatUtils::VERSION_2:
             // Version 2 dictionary writing is not supported.
             return false;
+        case FormatUtils::VERSION_4_ONLY_FOR_TESTING:
         case FormatUtils::VERSION_4:
-            return buffer->writeUintAndAdvancePosition(FormatUtils::VERSION_4 /* data */,
+            return buffer->writeUintAndAdvancePosition(version /* data */,
                     HEADER_DICTIONARY_VERSION_SIZE, writingPos);
         default:
             return false;
diff --git a/native/jni/src/suggest/policyimpl/dictionary/structure/dictionary_structure_with_buffer_policy_factory.cpp b/native/jni/src/suggest/policyimpl/dictionary/structure/dictionary_structure_with_buffer_policy_factory.cpp
index be7e43b..c4d1860 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/structure/dictionary_structure_with_buffer_policy_factory.cpp
+++ b/native/jni/src/suggest/policyimpl/dictionary/structure/dictionary_structure_with_buffer_policy_factory.cpp
@@ -52,9 +52,11 @@
         DictionaryStructureWithBufferPolicyFactory:: newPolicyForOnMemoryDict(
                 const int formatVersion, const std::vector<int> &locale,
                 const DictionaryHeaderStructurePolicy::AttributeMap *const attributeMap) {
-    switch (formatVersion) {
+    FormatUtils::FORMAT_VERSION dictFormatVersion = FormatUtils::getFormatVersion(formatVersion);
+    switch (dictFormatVersion) {
+        case FormatUtils::VERSION_4_ONLY_FOR_TESTING:
         case FormatUtils::VERSION_4: {
-            HeaderPolicy headerPolicy(FormatUtils::VERSION_4, locale, attributeMap);
+            HeaderPolicy headerPolicy(dictFormatVersion, locale, attributeMap);
             Ver4DictBuffers::Ver4DictBuffersPtr dictBuffers =
                     Ver4DictBuffers::createVer4DictBuffers(&headerPolicy,
                             Ver4DictConstants::MAX_DICT_EXTENDED_REGION_SIZE);
@@ -87,11 +89,13 @@
     if (!mmappedBuffer) {
         return DictionaryStructureWithBufferPolicy::StructurePolicyPtr(nullptr);
     }
-    switch (FormatUtils::detectFormatVersion(mmappedBuffer->getBuffer(),
-            mmappedBuffer->getBufferSize())) {
+    const FormatUtils::FORMAT_VERSION formatVersion = FormatUtils::detectFormatVersion(
+            mmappedBuffer->getBuffer(), mmappedBuffer->getBufferSize());
+    switch (formatVersion) {
         case FormatUtils::VERSION_2:
             AKLOGE("Given path is a directory but the format is version 2. path: %s", path);
             break;
+        case FormatUtils::VERSION_4_ONLY_FOR_TESTING:
         case FormatUtils::VERSION_4: {
             const int dictDirPathBufSize = strlen(headerFilePath) + 1 /* terminator */;
             char dictPath[dictDirPathBufSize];
@@ -102,7 +106,8 @@
                 return DictionaryStructureWithBufferPolicy::StructurePolicyPtr(nullptr);
             }
             Ver4DictBuffers::Ver4DictBuffersPtr dictBuffers(
-                    Ver4DictBuffers::openVer4DictBuffers(dictPath, std::move(mmappedBuffer)));
+                    Ver4DictBuffers::openVer4DictBuffers(dictPath, std::move(mmappedBuffer),
+                            formatVersion));
             if (!dictBuffers || !dictBuffers->isValid()) {
                 AKLOGE("DICT: The dictionary doesn't satisfy ver4 format requirements. path: %s",
                         path);
@@ -135,6 +140,7 @@
         case FormatUtils::VERSION_2:
             return DictionaryStructureWithBufferPolicy::StructurePolicyPtr(
                     new PatriciaTriePolicy(std::move(mmappedBuffer)));
+        case FormatUtils::VERSION_4_ONLY_FOR_TESTING:
         case FormatUtils::VERSION_4:
             AKLOGE("Given path is a file but the format is version 4. path: %s", path);
             break;
diff --git a/native/jni/src/suggest/policyimpl/dictionary/structure/pt_common/dynamic_pt_updating_helper.cpp b/native/jni/src/suggest/policyimpl/dictionary/structure/pt_common/dynamic_pt_updating_helper.cpp
index e02dd55..a527f03 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/structure/pt_common/dynamic_pt_updating_helper.cpp
+++ b/native/jni/src/suggest/policyimpl/dictionary/structure/pt_common/dynamic_pt_updating_helper.cpp
@@ -16,6 +16,7 @@
 
 #include "suggest/policyimpl/dictionary/structure/pt_common/dynamic_pt_updating_helper.h"
 
+#include "suggest/core/dictionary/property/unigram_property.h"
 #include "suggest/policyimpl/dictionary/structure/pt_common/dynamic_pt_reading_helper.h"
 #include "suggest/policyimpl/dictionary/structure/pt_common/dynamic_pt_writing_utils.h"
 #include "suggest/policyimpl/dictionary/structure/pt_common/patricia_trie_reading_utils.h"
@@ -29,9 +30,8 @@
 
 bool DynamicPtUpdatingHelper::addUnigramWord(
         DynamicPtReadingHelper *const readingHelper,
-        const int *const wordCodePoints, const int codePointCount, const int probability,
-        const bool isNotAWord, const bool isBlacklisted, const int timestamp,
-        bool *const outAddedNewUnigram) {
+        const int *const wordCodePoints, const int codePointCount,
+        const UnigramProperty *const unigramProperty, bool *const outAddedNewUnigram) {
     int parentPos = NOT_A_DICT_POS;
     while (!readingHelper->isEnd()) {
         const PtNodeParams ptNodeParams(readingHelper->getPtNodeParams());
@@ -53,20 +53,18 @@
             if (nextIndex >= codePointCount || !readingHelper->isMatchedCodePoint(ptNodeParams, j,
                     wordCodePoints[matchedCodePointCount + j])) {
                 *outAddedNewUnigram = true;
-                return reallocatePtNodeAndAddNewPtNodes(&ptNodeParams, j, isNotAWord, isBlacklisted,
-                        probability, timestamp, wordCodePoints + matchedCodePointCount,
+                return reallocatePtNodeAndAddNewPtNodes(&ptNodeParams, j, unigramProperty,
+                        wordCodePoints + matchedCodePointCount,
                         codePointCount - matchedCodePointCount);
             }
         }
         // All characters are matched.
         if (codePointCount == readingHelper->getTotalCodePointCount(ptNodeParams)) {
-            return setPtNodeProbability(&ptNodeParams, isNotAWord, isBlacklisted, probability,
-                    timestamp, outAddedNewUnigram);
+            return setPtNodeProbability(&ptNodeParams, unigramProperty, outAddedNewUnigram);
         }
         if (!ptNodeParams.hasChildren()) {
             *outAddedNewUnigram = true;
-            return createChildrenPtNodeArrayAndAChildPtNode(&ptNodeParams,
-                    isNotAWord, isBlacklisted, probability, timestamp,
+            return createChildrenPtNodeArrayAndAChildPtNode(&ptNodeParams, unigramProperty,
                     wordCodePoints + readingHelper->getTotalCodePointCount(ptNodeParams),
                     codePointCount - readingHelper->getTotalCodePointCount(ptNodeParams));
         }
@@ -83,7 +81,7 @@
     return createAndInsertNodeIntoPtNodeArray(parentPos,
             wordCodePoints + readingHelper->getPrevTotalCodePointCount(),
             codePointCount - readingHelper->getPrevTotalCodePointCount(),
-            isNotAWord, isBlacklisted, probability, timestamp, &pos);
+            unigramProperty, &pos);
 }
 
 bool DynamicPtUpdatingHelper::addBigramWords(const int word0Pos, const int word1Pos,
@@ -115,36 +113,34 @@
 
 bool DynamicPtUpdatingHelper::createAndInsertNodeIntoPtNodeArray(const int parentPos,
         const int *const nodeCodePoints, const int nodeCodePointCount,
-        const bool isNotAWord, const bool isBlacklisted, const int probability,
-        const int timestamp,  int *const forwardLinkFieldPos) {
+        const UnigramProperty *const unigramProperty, int *const forwardLinkFieldPos) {
     const int newPtNodeArrayPos = mBuffer->getTailPosition();
     if (!DynamicPtWritingUtils::writeForwardLinkPositionAndAdvancePosition(mBuffer,
             newPtNodeArrayPos, forwardLinkFieldPos)) {
         return false;
     }
     return createNewPtNodeArrayWithAChildPtNode(parentPos, nodeCodePoints, nodeCodePointCount,
-            isNotAWord, isBlacklisted, probability, timestamp);
+            unigramProperty);
 }
 
-bool DynamicPtUpdatingHelper::setPtNodeProbability(
-        const PtNodeParams *const originalPtNodeParams, const bool isNotAWord,
-        const bool isBlacklisted, const int probability, const int timestamp,
-        bool *const outAddedNewUnigram) {
+bool DynamicPtUpdatingHelper::setPtNodeProbability(const PtNodeParams *const originalPtNodeParams,
+        const UnigramProperty *const unigramProperty, bool *const outAddedNewUnigram) {
     if (originalPtNodeParams->isTerminal()) {
         // Overwrites the probability.
         *outAddedNewUnigram = false;
-        return mPtNodeWriter->updatePtNodeProbability(originalPtNodeParams, probability, timestamp);
+        return mPtNodeWriter->updatePtNodeUnigramProperty(originalPtNodeParams, unigramProperty);
     } else {
         // Make the node terminal and write the probability.
         *outAddedNewUnigram = true;
         const int movedPos = mBuffer->getTailPosition();
         int writingPos = movedPos;
         const PtNodeParams ptNodeParamsToWrite(getUpdatedPtNodeParams(originalPtNodeParams,
-                isNotAWord, isBlacklisted, true /* isTerminal */,
-                originalPtNodeParams->getParentPos(), originalPtNodeParams->getCodePointCount(),
-                originalPtNodeParams->getCodePoints(), probability));
+                unigramProperty->isNotAWord(), unigramProperty->isBlacklisted(),
+                true /* isTerminal */, originalPtNodeParams->getParentPos(),
+                originalPtNodeParams->getCodePointCount(), originalPtNodeParams->getCodePoints(),
+                unigramProperty->getProbability()));
         if (!mPtNodeWriter->writeNewTerminalPtNodeAndAdvancePosition(&ptNodeParamsToWrite,
-                timestamp, &writingPos)) {
+                unigramProperty, &writingPos)) {
             return false;
         }
         if (!mPtNodeWriter->markPtNodeAsMoved(originalPtNodeParams, movedPos, movedPos)) {
@@ -155,31 +151,30 @@
 }
 
 bool DynamicPtUpdatingHelper::createChildrenPtNodeArrayAndAChildPtNode(
-        const PtNodeParams *const parentPtNodeParams, const bool isNotAWord,
-        const bool isBlacklisted, const int probability, const int timestamp,
+        const PtNodeParams *const parentPtNodeParams, const UnigramProperty *const unigramProperty,
         const int *const codePoints, const int codePointCount) {
     const int newPtNodeArrayPos = mBuffer->getTailPosition();
     if (!mPtNodeWriter->updateChildrenPosition(parentPtNodeParams, newPtNodeArrayPos)) {
         return false;
     }
     return createNewPtNodeArrayWithAChildPtNode(parentPtNodeParams->getHeadPos(), codePoints,
-            codePointCount, isNotAWord, isBlacklisted, probability, timestamp);
+            codePointCount, unigramProperty);
 }
 
 bool DynamicPtUpdatingHelper::createNewPtNodeArrayWithAChildPtNode(
         const int parentPtNodePos, const int *const nodeCodePoints, const int nodeCodePointCount,
-        const bool isNotAWord, const bool isBlacklisted, const int probability,
-        const int timestamp) {
+        const UnigramProperty *const unigramProperty) {
     int writingPos = mBuffer->getTailPosition();
     if (!DynamicPtWritingUtils::writePtNodeArraySizeAndAdvancePosition(mBuffer,
             1 /* arraySize */, &writingPos)) {
         return false;
     }
     const PtNodeParams ptNodeParamsToWrite(getPtNodeParamsForNewPtNode(
-            isNotAWord, isBlacklisted, true /* isTerminal */,
-            parentPtNodePos, nodeCodePointCount, nodeCodePoints, probability));
-    if (!mPtNodeWriter->writeNewTerminalPtNodeAndAdvancePosition(&ptNodeParamsToWrite, timestamp,
-            &writingPos)) {
+            unigramProperty->isNotAWord(), unigramProperty->isBlacklisted(), true /* isTerminal */,
+            parentPtNodePos, nodeCodePointCount, nodeCodePoints,
+            unigramProperty->getProbability()));
+    if (!mPtNodeWriter->writeNewTerminalPtNodeAndAdvancePosition(&ptNodeParamsToWrite,
+            unigramProperty, &writingPos)) {
         return false;
     }
     if (!DynamicPtWritingUtils::writeForwardLinkPositionAndAdvancePosition(mBuffer,
@@ -192,13 +187,13 @@
 // Returns whether the dictionary updating was succeeded or not.
 bool DynamicPtUpdatingHelper::reallocatePtNodeAndAddNewPtNodes(
         const PtNodeParams *const reallocatingPtNodeParams, const int overlappingCodePointCount,
-        const bool isNotAWord, const bool isBlacklisted, const int probabilityOfNewPtNode,
-        const int timestamp, const int *const newNodeCodePoints, const int newNodeCodePointCount) {
+        const UnigramProperty *const unigramProperty, const int *const newNodeCodePoints,
+        const int newNodeCodePointCount) {
     // When addsExtraChild is true, split the reallocating PtNode and add new child.
     // Reallocating PtNode: abcde, newNode: abcxy.
     // abc (1st, not terminal) __ de (2nd)
     //                         \_ xy (extra child, terminal)
-    // Otherwise, this method makes 1st part terminal and write probabilityOfNewPtNode.
+    // Otherwise, this method makes 1st part terminal and write information in unigramProperty.
     // Reallocating PtNode: abcde, newNode: abc.
     // abc (1st, terminal) __ de (2nd)
     const bool addsExtraChild = newNodeCodePointCount > overlappingCodePointCount;
@@ -216,11 +211,12 @@
         }
     } else {
         const PtNodeParams ptNodeParamsToWrite(getPtNodeParamsForNewPtNode(
-                isNotAWord, isBlacklisted, true /* isTerminal */,
-                reallocatingPtNodeParams->getParentPos(), overlappingCodePointCount,
-                reallocatingPtNodeParams->getCodePoints(), probabilityOfNewPtNode));
+                unigramProperty->isNotAWord(), unigramProperty->isBlacklisted(),
+                true /* isTerminal */, reallocatingPtNodeParams->getParentPos(),
+                overlappingCodePointCount, reallocatingPtNodeParams->getCodePoints(),
+                unigramProperty->getProbability()));
         if (!mPtNodeWriter->writeNewTerminalPtNodeAndAdvancePosition(&ptNodeParamsToWrite,
-                timestamp, &writingPos)) {
+                unigramProperty, &writingPos)) {
             return false;
         }
     }
@@ -244,11 +240,12 @@
     }
     if (addsExtraChild) {
         const PtNodeParams extraChildPtNodeParams(getPtNodeParamsForNewPtNode(
-                isNotAWord, isBlacklisted, true /* isTerminal */,
-                firstPartOfReallocatedPtNodePos, newNodeCodePointCount - overlappingCodePointCount,
-                newNodeCodePoints + overlappingCodePointCount, probabilityOfNewPtNode));
+                unigramProperty->isNotAWord(), unigramProperty->isBlacklisted(),
+                true /* isTerminal */, firstPartOfReallocatedPtNodePos,
+                newNodeCodePointCount - overlappingCodePointCount,
+                newNodeCodePoints + overlappingCodePointCount, unigramProperty->getProbability()));
         if (!mPtNodeWriter->writeNewTerminalPtNodeAndAdvancePosition(&extraChildPtNodeParams,
-                timestamp, &writingPos)) {
+                unigramProperty, &writingPos)) {
             return false;
         }
     }
@@ -269,8 +266,8 @@
 }
 
 const PtNodeParams DynamicPtUpdatingHelper::getUpdatedPtNodeParams(
-        const PtNodeParams *const originalPtNodeParams, const bool isNotAWord,
-        const bool isBlacklisted, const bool isTerminal, const int parentPos,
+        const PtNodeParams *const originalPtNodeParams,
+        const bool isNotAWord, const bool isBlacklisted, const bool isTerminal, const int parentPos,
         const int codePointCount, const int *const codePoints, const int probability) const {
     const PatriciaTrieReadingUtils::NodeFlags flags = PatriciaTrieReadingUtils::createAndGetFlags(
             isBlacklisted, isNotAWord, isTerminal, originalPtNodeParams->hasShortcutTargets(),
diff --git a/native/jni/src/suggest/policyimpl/dictionary/structure/pt_common/dynamic_pt_updating_helper.h b/native/jni/src/suggest/policyimpl/dictionary/structure/pt_common/dynamic_pt_updating_helper.h
index 9b28152..44914fe 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/structure/pt_common/dynamic_pt_updating_helper.h
+++ b/native/jni/src/suggest/policyimpl/dictionary/structure/pt_common/dynamic_pt_updating_helper.h
@@ -26,6 +26,7 @@
 class DynamicPtReadingHelper;
 class PtNodeReader;
 class PtNodeWriter;
+class UnigramProperty;
 
 class DynamicPtUpdatingHelper {
  public:
@@ -37,9 +38,8 @@
 
     // Add a word to the dictionary. If the word already exists, update the probability.
     bool addUnigramWord(DynamicPtReadingHelper *const readingHelper,
-            const int *const wordCodePoints, const int codePointCount, const int probability,
-            const bool isNotAWord, const bool isBlacklisted, const int timestamp,
-            bool *const outAddedNewUnigram);
+            const int *const wordCodePoints, const int codePointCount,
+            const UnigramProperty *const unigramProperty, bool *const outAddedNewUnigram);
 
     // Add a bigram relation from word0Pos to word1Pos.
     bool addBigramWords(const int word0Pos, const int word1Pos, const int probability,
@@ -62,25 +62,22 @@
     PtNodeWriter *const mPtNodeWriter;
 
     bool createAndInsertNodeIntoPtNodeArray(const int parentPos, const int *const nodeCodePoints,
-            const int nodeCodePointCount, const bool isNotAWord, const bool isBlacklisted,
-            const int probability, const int timestamp, int *const forwardLinkFieldPos);
+            const int nodeCodePointCount, const UnigramProperty *const unigramProperty,
+            int *const forwardLinkFieldPos);
 
-    bool setPtNodeProbability(const PtNodeParams *const originalPtNodeParams, const bool isNotAWord,
-            const bool isBlacklisted, const int probability, const int timestamp,
-            bool *const outAddedNewUnigram);
+    bool setPtNodeProbability(const PtNodeParams *const originalPtNodeParams,
+            const UnigramProperty *const unigramProperty, bool *const outAddedNewUnigram);
 
     bool createChildrenPtNodeArrayAndAChildPtNode(const PtNodeParams *const parentPtNodeParams,
-            const bool isNotAWord, const bool isBlacklisted, const int probability,
-            const int timestamp, const int *const codePoints, const int codePointCount);
+            const UnigramProperty *const unigramProperty, const int *const codePoints,
+            const int codePointCount);
 
     bool createNewPtNodeArrayWithAChildPtNode(const int parentPos, const int *const nodeCodePoints,
-            const int nodeCodePointCount, const bool isNotAWord, const bool isBlacklisted,
-            const int probability, const int timestamp);
+            const int nodeCodePointCount, const UnigramProperty *const unigramProperty);
 
     bool reallocatePtNodeAndAddNewPtNodes(
             const PtNodeParams *const reallocatingPtNodeParams, const int overlappingCodePointCount,
-            const bool isNotAWord, const bool isBlacklisted, const int probabilityOfNewPtNode,
-            const int timestamp, const int *const newNodeCodePoints,
+            const UnigramProperty *const unigramProperty, const int *const newNodeCodePoints,
             const int newNodeCodePointCount);
 
     const PtNodeParams getUpdatedPtNodeParams(const PtNodeParams *const originalPtNodeParams,
diff --git a/native/jni/src/suggest/policyimpl/dictionary/structure/pt_common/pt_node_writer.h b/native/jni/src/suggest/policyimpl/dictionary/structure/pt_common/pt_node_writer.h
index e843f07..cbca3fe 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/structure/pt_common/pt_node_writer.h
+++ b/native/jni/src/suggest/policyimpl/dictionary/structure/pt_common/pt_node_writer.h
@@ -24,6 +24,8 @@
 
 namespace latinime {
 
+class UnigramProperty;
+
 // Interface class used to write PtNode information.
 class PtNodeWriter {
  public:
@@ -51,8 +53,8 @@
     virtual bool markPtNodeAsWillBecomeNonTerminal(
             const PtNodeParams *const toBeUpdatedPtNodeParams) = 0;
 
-    virtual bool updatePtNodeProbability(const PtNodeParams *const toBeUpdatedPtNodeParams,
-            const int probability, const int timestamp) = 0;
+    virtual bool updatePtNodeUnigramProperty(const PtNodeParams *const toBeUpdatedPtNodeParams,
+            const UnigramProperty *const unigramProperty) = 0;
 
     virtual bool updatePtNodeProbabilityAndGetNeedsToKeepPtNodeAfterGC(
             const PtNodeParams *const toBeUpdatedPtNodeParams,
@@ -65,7 +67,7 @@
             int *const ptNodeWritingPos) = 0;
 
     virtual bool writeNewTerminalPtNodeAndAdvancePosition(const PtNodeParams *const ptNodeParams,
-            const int timestamp, int *const ptNodeWritingPos) = 0;
+            const UnigramProperty *const unigramProperty, int *const ptNodeWritingPos) = 0;
 
     virtual bool addNewBigramEntry(const PtNodeParams *const sourcePtNodeParams,
             const PtNodeParams *const targetPtNodeParam, const int probability, const int timestamp,
diff --git a/native/jni/src/suggest/policyimpl/dictionary/structure/v4/content/bigram_dict_content.h b/native/jni/src/suggest/policyimpl/dictionary/structure/v4/content/bigram_dict_content.h
index 40ece76..944e0f9 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/structure/v4/content/bigram_dict_content.h
+++ b/native/jni/src/suggest/policyimpl/dictionary/structure/v4/content/bigram_dict_content.h
@@ -88,6 +88,10 @@
             const BigramDictContent *const originalBigramDictContent,
             int *const outBigramEntryCount);
 
+    bool isContentTailPos(const int pos) const {
+        return pos == getContentBuffer()->getTailPosition();
+    }
+
  private:
     DISALLOW_COPY_AND_ASSIGN(BigramDictContent);
 
diff --git a/native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_dict_buffers.cpp b/native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_dict_buffers.cpp
index 95f6544..77ed38b 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_dict_buffers.cpp
+++ b/native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_dict_buffers.cpp
@@ -27,7 +27,8 @@
 namespace latinime {
 
 /* static */ Ver4DictBuffers::Ver4DictBuffersPtr Ver4DictBuffers::openVer4DictBuffers(
-        const char *const dictPath, MmappedBuffer::MmappedBufferPtr headerBuffer) {
+        const char *const dictPath, MmappedBuffer::MmappedBufferPtr headerBuffer,
+        const FormatUtils::FORMAT_VERSION formatVersion) {
     if (!headerBuffer) {
         ASSERT(false);
         AKLOGE("The header buffer must be valid to open ver4 dict buffers.");
@@ -35,7 +36,8 @@
     }
     // TODO: take only dictDirPath, and open both header and trie files in the constructor below
     const bool isUpdatable = headerBuffer->isUpdatable();
-    return Ver4DictBuffersPtr(new Ver4DictBuffers(dictPath, std::move(headerBuffer), isUpdatable));
+    return Ver4DictBuffersPtr(new Ver4DictBuffers(dictPath, std::move(headerBuffer), isUpdatable,
+            formatVersion));
 }
 
 bool Ver4DictBuffers::flushHeaderAndDictBuffers(const char *const dictDirPath,
@@ -113,11 +115,12 @@
 }
 
 Ver4DictBuffers::Ver4DictBuffers(const char *const dictPath,
-        MmappedBuffer::MmappedBufferPtr headerBuffer, const bool isUpdatable)
+        MmappedBuffer::MmappedBufferPtr headerBuffer, const bool isUpdatable,
+        const FormatUtils::FORMAT_VERSION formatVersion)
         : mHeaderBuffer(std::move(headerBuffer)),
           mDictBuffer(MmappedBuffer::openBuffer(dictPath,
                   Ver4DictConstants::TRIE_FILE_EXTENSION, isUpdatable)),
-          mHeaderPolicy(mHeaderBuffer->getBuffer(), FormatUtils::VERSION_4),
+          mHeaderPolicy(mHeaderBuffer->getBuffer(), formatVersion),
           mExpandableHeaderBuffer(mHeaderBuffer ? mHeaderBuffer->getBuffer() : nullptr,
                   mHeaderPolicy.getSize(),
                   BufferWithExtendableBuffer::DEFAULT_MAX_ADDITIONAL_BUFFER_SIZE),
diff --git a/native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_dict_buffers.h b/native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_dict_buffers.h
index fc41432..df177c1 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_dict_buffers.h
+++ b/native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_dict_buffers.h
@@ -36,7 +36,8 @@
     typedef std::unique_ptr<Ver4DictBuffers> Ver4DictBuffersPtr;
 
     static Ver4DictBuffersPtr openVer4DictBuffers(const char *const dictDirPath,
-            MmappedBuffer::MmappedBufferPtr headerBuffer);
+            MmappedBuffer::MmappedBufferPtr headerBuffer,
+            const FormatUtils::FORMAT_VERSION formatVersion);
 
     static AK_FORCE_INLINE Ver4DictBuffersPtr createVer4DictBuffers(
             const HeaderPolicy *const headerPolicy, const int maxTrieSize) {
@@ -120,7 +121,8 @@
     DISALLOW_COPY_AND_ASSIGN(Ver4DictBuffers);
 
     Ver4DictBuffers(const char *const dictDirPath,
-            const MmappedBuffer::MmappedBufferPtr headerBuffer, const bool isUpdatable);
+            const MmappedBuffer::MmappedBufferPtr headerBuffer, const bool isUpdatable,
+            const FormatUtils::FORMAT_VERSION formatVersion);
 
     Ver4DictBuffers(const HeaderPolicy *const headerPolicy, const int maxTrieSize);
 
diff --git a/native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_patricia_trie_node_writer.cpp b/native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_patricia_trie_node_writer.cpp
index 38ff42f..50a3e56 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_patricia_trie_node_writer.cpp
+++ b/native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_patricia_trie_node_writer.cpp
@@ -16,6 +16,7 @@
 
 #include "suggest/policyimpl/dictionary/structure/v4/ver4_patricia_trie_node_writer.h"
 
+#include "suggest/core/dictionary/property/unigram_property.h"
 #include "suggest/policyimpl/dictionary/bigram/ver4_bigram_list_policy.h"
 #include "suggest/policyimpl/dictionary/header/header_policy.h"
 #include "suggest/policyimpl/dictionary/shortcut/ver4_shortcut_list_policy.h"
@@ -133,9 +134,11 @@
             &writingPos);
 }
 
-bool Ver4PatriciaTrieNodeWriter::updatePtNodeProbability(
-        const PtNodeParams *const toBeUpdatedPtNodeParams, const int newProbability,
-        const int timestamp) {
+bool Ver4PatriciaTrieNodeWriter::updatePtNodeUnigramProperty(
+        const PtNodeParams *const toBeUpdatedPtNodeParams,
+        const UnigramProperty *const unigramProperty) {
+    // Update probability and historical information.
+    // TODO: Update other information in the unigram property.
     if (!toBeUpdatedPtNodeParams->isTerminal()) {
         return false;
     }
@@ -143,7 +146,7 @@
             mBuffers->getProbabilityDictContent()->getProbabilityEntry(
                     toBeUpdatedPtNodeParams->getTerminalId());
     const ProbabilityEntry probabilityEntry = createUpdatedEntryFrom(&originalProbabilityEntry,
-            newProbability, timestamp);
+            unigramProperty);
     return mBuffers->getMutableProbabilityDictContent()->setProbabilityEntry(
             toBeUpdatedPtNodeParams->getTerminalId(), &probabilityEntry);
 }
@@ -204,7 +207,8 @@
 
 
 bool Ver4PatriciaTrieNodeWriter::writeNewTerminalPtNodeAndAdvancePosition(
-        const PtNodeParams *const ptNodeParams, const int timestamp, int *const ptNodeWritingPos) {
+        const PtNodeParams *const ptNodeParams, const UnigramProperty *const unigramProperty,
+        int *const ptNodeWritingPos) {
     int terminalId = Ver4DictConstants::NOT_A_TERMINAL_ID;
     if (!writePtNodeAndGetTerminalIdAndAdvancePosition(ptNodeParams, &terminalId,
             ptNodeWritingPos)) {
@@ -213,7 +217,7 @@
     // Write probability.
     ProbabilityEntry newProbabilityEntry;
     const ProbabilityEntry probabilityEntryToWrite = createUpdatedEntryFrom(
-            &newProbabilityEntry, ptNodeParams->getProbability(), timestamp);
+            &newProbabilityEntry, unigramProperty);
     return mBuffers->getMutableProbabilityDictContent()->setProbabilityEntry(terminalId,
             &probabilityEntryToWrite);
 }
@@ -379,18 +383,20 @@
 }
 
 const ProbabilityEntry Ver4PatriciaTrieNodeWriter::createUpdatedEntryFrom(
-        const ProbabilityEntry *const originalProbabilityEntry, const int newProbability,
-        const int timestamp) const {
+        const ProbabilityEntry *const originalProbabilityEntry,
+        const UnigramProperty *const unigramProperty) const {
     // TODO: Consolidate historical info and probability.
     if (mHeaderPolicy->hasHistoricalInfoOfWords()) {
         const HistoricalInfo updatedHistoricalInfo =
                 ForgettingCurveUtils::createUpdatedHistoricalInfo(
-                        originalProbabilityEntry->getHistoricalInfo(), newProbability, timestamp,
+                        originalProbabilityEntry->getHistoricalInfo(),
+                        unigramProperty->getProbability(), unigramProperty->getTimestamp(),
                         mHeaderPolicy);
         return originalProbabilityEntry->createEntryWithUpdatedHistoricalInfo(
                 &updatedHistoricalInfo);
     } else {
-        return originalProbabilityEntry->createEntryWithUpdatedProbability(newProbability);
+        return originalProbabilityEntry->createEntryWithUpdatedProbability(
+                unigramProperty->getProbability());
     }
 }
 
diff --git a/native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_patricia_trie_node_writer.h b/native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_patricia_trie_node_writer.h
index b2b0504..f20d3a2 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_patricia_trie_node_writer.h
+++ b/native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_patricia_trie_node_writer.h
@@ -57,8 +57,8 @@
     virtual bool markPtNodeAsWillBecomeNonTerminal(
             const PtNodeParams *const toBeUpdatedPtNodeParams);
 
-    virtual bool updatePtNodeProbability(const PtNodeParams *const toBeUpdatedPtNodeParams,
-            const int newProbability, const int timestamp);
+    virtual bool updatePtNodeUnigramProperty(const PtNodeParams *const toBeUpdatedPtNodeParams,
+            const UnigramProperty *const unigramProperty);
 
     virtual bool updatePtNodeProbabilityAndGetNeedsToKeepPtNodeAfterGC(
             const PtNodeParams *const toBeUpdatedPtNodeParams, bool *const outNeedsToKeepPtNode);
@@ -73,7 +73,7 @@
             int *const ptNodeWritingPos);
 
     virtual bool writeNewTerminalPtNodeAndAdvancePosition(const PtNodeParams *const ptNodeParams,
-            const int timestamp, int *const ptNodeWritingPos);
+            const UnigramProperty *const unigramProperty, int *const ptNodeWritingPos);
 
     virtual bool addNewBigramEntry(const PtNodeParams *const sourcePtNodeParams,
             const PtNodeParams *const targetPtNodeParam, const int probability, const int timestamp,
@@ -102,11 +102,12 @@
             const PtNodeParams *const ptNodeParams, int *const outTerminalId,
             int *const ptNodeWritingPos);
 
-    // Create updated probability entry using given probability and timestamp. In addition to the
+    // Create updated probability entry using given unigram property. In addition to the
     // probability, this method updates historical information if needed.
+    // TODO: Update flags belonging to the unigram property.
     const ProbabilityEntry createUpdatedEntryFrom(
-            const ProbabilityEntry *const originalProbabilityEntry, const int newProbability,
-            const int timestamp) const;
+            const ProbabilityEntry *const originalProbabilityEntry,
+            const UnigramProperty *const unigramProperty) const;
 
     bool updatePtNodeFlags(const int ptNodePos, const bool isBlacklisted, const bool isNotAWord,
             const bool isTerminal, const bool hasShortcutTargets, const bool hasBigrams,
diff --git a/native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_patricia_trie_policy.cpp b/native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_patricia_trie_policy.cpp
index bbfd22e..2584fe5 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_patricia_trie_policy.cpp
+++ b/native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_patricia_trie_policy.cpp
@@ -179,9 +179,7 @@
     readingHelper.initWithPtNodeArrayPos(getRootPosition());
     bool addedNewUnigram = false;
     if (mUpdatingHelper.addUnigramWord(&readingHelper, word, length,
-            unigramProperty->getProbability(), unigramProperty->isNotAWord(),
-            unigramProperty->isBlacklisted(), unigramProperty->getTimestamp(),
-            &addedNewUnigram)) {
+            unigramProperty, &addedNewUnigram)) {
         if (addedNewUnigram) {
             mUnigramCount++;
         }
diff --git a/native/jni/src/suggest/policyimpl/dictionary/utils/dict_file_writing_utils.cpp b/native/jni/src/suggest/policyimpl/dictionary/utils/dict_file_writing_utils.cpp
index 87fa599..7bc7b0a 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/utils/dict_file_writing_utils.cpp
+++ b/native/jni/src/suggest/policyimpl/dictionary/utils/dict_file_writing_utils.cpp
@@ -34,9 +34,12 @@
         const int dictVersion, const std::vector<int> localeAsCodePointVector,
         const DictionaryHeaderStructurePolicy::AttributeMap *const attributeMap) {
     TimeKeeper::setCurrentTime();
-    switch (dictVersion) {
+    const FormatUtils::FORMAT_VERSION formatVersion = FormatUtils::getFormatVersion(dictVersion);
+    switch (formatVersion) {
+        case FormatUtils::VERSION_4_ONLY_FOR_TESTING:
         case FormatUtils::VERSION_4:
-            return createEmptyV4DictFile(filePath, localeAsCodePointVector, attributeMap);
+            return createEmptyV4DictFile(filePath, localeAsCodePointVector, attributeMap,
+                    formatVersion);
         default:
             AKLOGE("Cannot create dictionary %s because format version %d is not supported.",
                     filePath, dictVersion);
@@ -46,8 +49,9 @@
 
 /* static */ bool DictFileWritingUtils::createEmptyV4DictFile(const char *const dirPath,
         const std::vector<int> localeAsCodePointVector,
-        const DictionaryHeaderStructurePolicy::AttributeMap *const attributeMap) {
-    HeaderPolicy headerPolicy(FormatUtils::VERSION_4, localeAsCodePointVector, attributeMap);
+        const DictionaryHeaderStructurePolicy::AttributeMap *const attributeMap,
+        const FormatUtils::FORMAT_VERSION formatVersion) {
+    HeaderPolicy headerPolicy(formatVersion, localeAsCodePointVector, attributeMap);
     Ver4DictBuffers::Ver4DictBuffersPtr dictBuffers(
             Ver4DictBuffers::createVer4DictBuffers(&headerPolicy,
                     Ver4DictConstants::MAX_DICT_EXTENDED_REGION_SIZE));
diff --git a/native/jni/src/suggest/policyimpl/dictionary/utils/dict_file_writing_utils.h b/native/jni/src/suggest/policyimpl/dictionary/utils/dict_file_writing_utils.h
index 54ec651..a822989 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/utils/dict_file_writing_utils.h
+++ b/native/jni/src/suggest/policyimpl/dictionary/utils/dict_file_writing_utils.h
@@ -21,6 +21,7 @@
 
 #include "defines.h"
 #include "suggest/policyimpl/dictionary/header/header_read_write_utils.h"
+#include "suggest/policyimpl/dictionary/utils/format_utils.h"
 
 namespace latinime {
 
@@ -46,7 +47,8 @@
 
     static bool createEmptyV4DictFile(const char *const filePath,
             const std::vector<int> localeAsCodePointVector,
-            const DictionaryHeaderStructurePolicy::AttributeMap *const attributeMap);
+            const DictionaryHeaderStructurePolicy::AttributeMap *const attributeMap,
+            const FormatUtils::FORMAT_VERSION formatVersion);
 
     static bool flushBufferToFile(const char *const filePath,
             const BufferWithExtendableBuffer *const buffer);
diff --git a/native/jni/src/suggest/policyimpl/dictionary/utils/format_utils.cpp b/native/jni/src/suggest/policyimpl/dictionary/utils/format_utils.cpp
index cd3c403..a8518cd 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/utils/format_utils.cpp
+++ b/native/jni/src/suggest/policyimpl/dictionary/utils/format_utils.cpp
@@ -25,6 +25,18 @@
 // Magic number (4 bytes), version (2 bytes), flags (2 bytes), header size (4 bytes) = 12
 const int FormatUtils::DICTIONARY_MINIMUM_SIZE = 12;
 
+/* static */ FormatUtils::FORMAT_VERSION FormatUtils::getFormatVersion(const int formatVersion) {
+    switch (formatVersion) {
+        case VERSION_2:
+            return VERSION_2;
+        case VERSION_4_ONLY_FOR_TESTING:
+            return VERSION_4_ONLY_FOR_TESTING;
+        case VERSION_4:
+            return VERSION_4;
+        default:
+            return UNKNOWN_VERSION;
+    }
+}
 /* static */ FormatUtils::FORMAT_VERSION FormatUtils::detectFormatVersion(
         const uint8_t *const dict, const int dictSize) {
     // The magic number is stored big-endian.
@@ -46,6 +58,8 @@
             // same so we use them for both here.
             if (ByteArrayUtils::readUint16(dict, 4) == VERSION_2) {
                 return VERSION_2;
+            } else if (ByteArrayUtils::readUint16(dict, 4) == VERSION_4_ONLY_FOR_TESTING) {
+                return VERSION_4_ONLY_FOR_TESTING;
             } else if (ByteArrayUtils::readUint16(dict, 4) == VERSION_4) {
                 return VERSION_4;
             } else {
diff --git a/native/jni/src/suggest/policyimpl/dictionary/utils/format_utils.h b/native/jni/src/suggest/policyimpl/dictionary/utils/format_utils.h
index 759b1c9..20dfb9d 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/utils/format_utils.h
+++ b/native/jni/src/suggest/policyimpl/dictionary/utils/format_utils.h
@@ -31,6 +31,7 @@
     enum FORMAT_VERSION {
         // These MUST have the same values as the relevant constants in FormatSpec.java.
         VERSION_2 = 2,
+        VERSION_4_ONLY_FOR_TESTING = 399,
         VERSION_4 = 401,
         UNKNOWN_VERSION = -1
     };
@@ -39,6 +40,7 @@
     // unsupported or obsolete dictionary formats.
     static const uint32_t MAGIC_NUMBER;
 
+    static FORMAT_VERSION getFormatVersion(const int formatVersion);
     static FORMAT_VERSION detectFormatVersion(const uint8_t *const dict, const int dictSize);
 
  private:
diff --git a/tests/src/com/android/inputmethod/keyboard/layout/tests/EnglishCustomizer.java b/tests/src/com/android/inputmethod/keyboard/layout/tests/EnglishCustomizer.java
index 29264ff..3e82f65 100644
--- a/tests/src/com/android/inputmethod/keyboard/layout/tests/EnglishCustomizer.java
+++ b/tests/src/com/android/inputmethod/keyboard/layout/tests/EnglishCustomizer.java
@@ -27,34 +27,34 @@
     @Override
     public ExpectedKeyboardBuilder setAccentedLetters(final ExpectedKeyboardBuilder builder) {
         return builder
-                // U+00E8: "è" LATIN SMALL LETTER E WITH GRAVE
                 // U+00E9: "é" LATIN SMALL LETTER E WITH ACUTE
+                // U+00E8: "è" LATIN SMALL LETTER E WITH GRAVE
                 // U+00EA: "ê" LATIN SMALL LETTER E WITH CIRCUMFLEX
                 // U+00EB: "ë" LATIN SMALL LETTER E WITH DIAERESIS
                 // U+0113: "ē" LATIN SMALL LETTER E WITH MACRON
-                .setMoreKeysOf("e", "\u00E8", "\u00E9", "\u00EA", "\u00EB", "\u0113")
+                .setMoreKeysOf("e", "\u00E9", "\u00E8", "\u00EA", "\u00EB", "\u0113")
+                // U+00FA: "ú" LATIN SMALL LETTER U WITH ACUTE
                 // U+00FB: "û" LATIN SMALL LETTER U WITH CIRCUMFLEX
                 // U+00FC: "ü" LATIN SMALL LETTER U WITH DIAERESIS
                 // U+00F9: "ù" LATIN SMALL LETTER U WITH GRAVE
-                // U+00FA: "ú" LATIN SMALL LETTER U WITH ACUTE
                 // U+016B: "ū" LATIN SMALL LETTER U WITH MACRON
-                .setMoreKeysOf("u", "\u00FB", "\u00FC", "\u00F9", "\u00FA", "\u016B")
+                .setMoreKeysOf("u", "\u00FA", "\u00FB", "\u00FC", "\u00F9", "\u016B")
+                // U+00ED: "í" LATIN SMALL LETTER I WITH ACUTE
                 // U+00EE: "î" LATIN SMALL LETTER I WITH CIRCUMFLEX
                 // U+00EF: "ï" LATIN SMALL LETTER I WITH DIAERESIS
-                // U+00ED: "í" LATIN SMALL LETTER I WITH ACUTE
                 // U+012B: "ī" LATIN SMALL LETTER I WITH MACRON
                 // U+00EC: "ì" LATIN SMALL LETTER I WITH GRAVE
-                .setMoreKeysOf("i", "\u00EE", "\u00EF", "\u00ED", "\u012B", "\u00EC")
+                .setMoreKeysOf("i", "\u00ED", "\u00EE", "\u00EF", "\u012B", "\u00EC")
+                // U+00F3: "ó" LATIN SMALL LETTER O WITH ACUTE
                 // U+00F4: "ô" LATIN SMALL LETTER O WITH CIRCUMFLEX
                 // U+00F6: "ö" LATIN SMALL LETTER O WITH DIAERESIS
                 // U+00F2: "ò" LATIN SMALL LETTER O WITH GRAVE
-                // U+00F3: "ó" LATIN SMALL LETTER O WITH ACUTE
                 // U+0153: "œ" LATIN SMALL LIGATURE OE
                 // U+00F8: "ø" LATIN SMALL LETTER O WITH STROKE
                 // U+014D: "ō" LATIN SMALL LETTER O WITH MACRON
                 // U+00F5: "õ" LATIN SMALL LETTER O WITH TILDE
                 .setMoreKeysOf("o",
-                        "\u00F4", "\u00F6", "\u00F2", "\u00F3", "\u0153", "\u00F8", "\u014D",
+                        "\u00F3", "\u00F4", "\u00F6", "\u00F2", "\u0153", "\u00F8", "\u014D",
                         "\u00F5")
                 // U+00E1: "á" LATIN SMALL LETTER A WITH ACUTE
                 // U+00E2: "â" LATIN SMALL LETTER A WITH CIRCUMFLEX
diff --git a/tests/src/com/android/inputmethod/latin/BinaryDictionaryTests.java b/tests/src/com/android/inputmethod/latin/BinaryDictionaryTests.java
index 0fb0fa5..9ceafa7 100644
--- a/tests/src/com/android/inputmethod/latin/BinaryDictionaryTests.java
+++ b/tests/src/com/android/inputmethod/latin/BinaryDictionaryTests.java
@@ -46,21 +46,23 @@
 
     private File createEmptyDictionaryAndGetFile(final String dictId,
             final int formatVersion) throws IOException {
-       if (formatVersion == FormatSpec.VERSION4) {
-            return createEmptyVer4DictionaryAndGetFile(dictId);
+        if (formatVersion == FormatSpec.VERSION4
+                || formatVersion == FormatSpec.VERSION4_ONLY_FOR_TESTING) {
+            return createEmptyVer4DictionaryAndGetFile(dictId, formatVersion);
         } else {
             throw new IOException("Dictionary format version " + formatVersion
                     + " is not supported.");
         }
     }
 
-    private File createEmptyVer4DictionaryAndGetFile(final String dictId) throws IOException {
+    private File createEmptyVer4DictionaryAndGetFile(final String dictId,
+            final int formatVersion) throws IOException {
         final File file = File.createTempFile(dictId, TEST_DICT_FILE_EXTENSION,
                 getContext().getCacheDir());
         file.delete();
         file.mkdir();
         Map<String, String> attributeMap = new HashMap<String, String>();
-        if (BinaryDictionaryUtils.createEmptyDictFile(file.getAbsolutePath(), FormatSpec.VERSION4,
+        if (BinaryDictionaryUtils.createEmptyDictFile(file.getAbsolutePath(), formatVersion,
                 Locale.ENGLISH, attributeMap)) {
             return file;
         } else {
@@ -1223,4 +1225,36 @@
             }
         }
     }
+
+    public void testDictMigration() {
+        testDictMigration(FormatSpec.VERSION4_ONLY_FOR_TESTING, FormatSpec.VERSION4);
+    }
+
+    private void testDictMigration(final int fromFormatVersion, final int toFormatVersion) {
+        File dictFile = null;
+        try {
+            dictFile = createEmptyDictionaryAndGetFile("TestBinaryDictionary", fromFormatVersion);
+        } catch (IOException e) {
+            fail("IOException while writing an initial dictionary : " + e);
+        }
+        final BinaryDictionary binaryDictionary = new BinaryDictionary(dictFile.getAbsolutePath(),
+                0 /* offset */, dictFile.length(), true /* useFullEditDistance */,
+                Locale.getDefault(), TEST_LOCALE, true /* isUpdatable */);
+        final int unigramProbability = 100;
+        addUnigramWord(binaryDictionary, "aaa", unigramProbability);
+        addUnigramWord(binaryDictionary, "bbb", unigramProbability);
+        final int bigramProbability = 10;
+        addBigramWords(binaryDictionary, "aaa", "bbb", bigramProbability);
+        assertEquals(unigramProbability, binaryDictionary.getFrequency("aaa"));
+        assertEquals(unigramProbability, binaryDictionary.getFrequency("bbb"));
+        assertTrue(binaryDictionary.isValidBigram("aaa", "bbb"));
+        assertEquals(fromFormatVersion, binaryDictionary.getFormatVersion());
+        assertTrue(binaryDictionary.migrateTo(toFormatVersion));
+        assertTrue(binaryDictionary.isValidDictionary());
+        assertEquals(toFormatVersion, binaryDictionary.getFormatVersion());
+        assertEquals(unigramProbability, binaryDictionary.getFrequency("aaa"));
+        assertEquals(unigramProbability, binaryDictionary.getFrequency("bbb"));
+        // TODO: Add tests for bigram frequency when the implementation gets ready.
+        assertTrue(binaryDictionary.isValidBigram("aaa", "bbb"));
+    }
 }
diff --git a/tools/make-keyboard-text/res/values-zu/donottranslate-more-keys.xml b/tools/make-keyboard-text/res/values-zu/donottranslate-more-keys.xml
index f9150f3..2c5df0c 100644
--- a/tools/make-keyboard-text/res/values-zu/donottranslate-more-keys.xml
+++ b/tools/make-keyboard-text/res/values-zu/donottranslate-more-keys.xml
@@ -28,33 +28,33 @@
          U+00E5: "å" LATIN SMALL LETTER A WITH RING ABOVE
          U+0101: "ā" LATIN SMALL LETTER A WITH MACRON -->
     <string name="morekeys_a">&#x00E0;,&#x00E1;,&#x00E2;,&#x00E4;,&#x00E6;,&#x00E3;,&#x00E5;,&#x0101;</string>
-    <!-- U+00E8: "è" LATIN SMALL LETTER E WITH GRAVE
-         U+00E9: "é" LATIN SMALL LETTER E WITH ACUTE
+    <!-- U+00E9: "é" LATIN SMALL LETTER E WITH ACUTE
+         U+00E8: "è" LATIN SMALL LETTER E WITH GRAVE
          U+00EA: "ê" LATIN SMALL LETTER E WITH CIRCUMFLEX
          U+00EB: "ë" LATIN SMALL LETTER E WITH DIAERESIS
          U+0113: "ē" LATIN SMALL LETTER E WITH MACRON -->
-    <string name="morekeys_e">&#x00E8;,&#x00E9;,&#x00EA;,&#x00EB;,&#x0113;</string>
-    <!-- U+00EE: "î" LATIN SMALL LETTER I WITH CIRCUMFLEX
+    <string name="morekeys_e">&#x00E9;,&#x00E8;,&#x00EA;,&#x00EB;,&#x0113;</string>
+    <!-- U+00ED: "í" LATIN SMALL LETTER I WITH ACUTE
+         U+00EE: "î" LATIN SMALL LETTER I WITH CIRCUMFLEX
          U+00EF: "ï" LATIN SMALL LETTER I WITH DIAERESIS
-         U+00ED: "í" LATIN SMALL LETTER I WITH ACUTE
          U+012B: "ī" LATIN SMALL LETTER I WITH MACRON
          U+00EC: "ì" LATIN SMALL LETTER I WITH GRAVE -->
-    <string name="morekeys_i">&#x00EE;,&#x00EF;,&#x00ED;,&#x012B;,&#x00EC;</string>
-    <!-- U+00F4: "ô" LATIN SMALL LETTER O WITH CIRCUMFLEX
+    <string name="morekeys_i">&#x00ED;,&#x00EE;,&#x00EF;,&#x012B;,&#x00EC;</string>
+    <!-- U+00F3: "ó" LATIN SMALL LETTER O WITH ACUTE
+         U+00F4: "ô" LATIN SMALL LETTER O WITH CIRCUMFLEX
          U+00F6: "ö" LATIN SMALL LETTER O WITH DIAERESIS
          U+00F2: "ò" LATIN SMALL LETTER O WITH GRAVE
-         U+00F3: "ó" LATIN SMALL LETTER O WITH ACUTE
          U+0153: "œ" LATIN SMALL LIGATURE OE
          U+00F8: "ø" LATIN SMALL LETTER O WITH STROKE
          U+014D: "ō" LATIN SMALL LETTER O WITH MACRON
          U+00F5: "õ" LATIN SMALL LETTER O WITH TILDE -->
-    <string name="morekeys_o">&#x00F4;,&#x00F6;,&#x00F2;,&#x00F3;,&#x0153;,&#x00F8;,&#x014D;,&#x00F5;</string>
-    <!-- U+00FB: "û" LATIN SMALL LETTER U WITH CIRCUMFLEX
+    <string name="morekeys_o">&#x00F3;,&#x00F4;,&#x00F6;,&#x00F2;,&#x0153;,&#x00F8;,&#x014D;,&#x00F5;</string>
+    <!-- U+00FA: "ú" LATIN SMALL LETTER U WITH ACUTE
+         U+00FB: "û" LATIN SMALL LETTER U WITH CIRCUMFLEX
          U+00FC: "ü" LATIN SMALL LETTER U WITH DIAERESIS
          U+00F9: "ù" LATIN SMALL LETTER U WITH GRAVE
-         U+00FA: "ú" LATIN SMALL LETTER U WITH ACUTE
          U+016B: "ū" LATIN SMALL LETTER U WITH MACRON -->
-    <string name="morekeys_u">&#x00FB;,&#x00FC;,&#x00F9;,&#x00FA;,&#x016B;</string>
+    <string name="morekeys_u">&#x00FA;,&#x00FB;,&#x00FC;,&#x00F9;,&#x016B;</string>
     <!-- U+00DF: "ß" LATIN SMALL LETTER SHARP S -->
     <string name="morekeys_s">&#x00DF;</string>
     <!-- U+00F1: "ñ" LATIN SMALL LETTER N WITH TILDE -->