Add "languageCode" attribute to "case" tag in Keyboard XML

bug: 3451586
Change-Id: I08ca80e48648ba18543e9b8ca7362c06bb61a826
diff --git a/java/res/values/attrs.xml b/java/res/values/attrs.xml
index dea1635..f5babd3 100644
--- a/java/res/values/attrs.xml
+++ b/java/res/values/attrs.xml
@@ -182,6 +182,7 @@
             <flag name="actionDone" value="6" />
             <flag name="actionPrevious" value="7" />
         </attr>
+        <attr name="languageCode" format="string" />
     </declare-styleable>
 
     <declare-styleable name="Keyboard_KeyStyle">