nsis: added support for pt-BR to installer and update README.txt

Prepare for PR #16692 which will eventually bring pt-br translation to
the installer and add some clarification on how to test the installer
with different languages

closes: #16725

Signed-off-by: RestorerZ <restorer@mail2k.ru>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/nsis/gvim.nsi b/nsis/gvim.nsi
index 878867f..4aa678f 100644
--- a/nsis/gvim.nsi
+++ b/nsis/gvim.nsi
@@ -1,6 +1,6 @@
 # NSIS file to create a self-installing exe for Vim.
 # It requires NSIS version 3.0 or later.
-# Last Change:	2025 Jan 05
+# Last Change:	2025 Feb 24
 
 Unicode true
 
@@ -806,7 +806,8 @@
   ClearErrors
   System::Call 'kernel32::GetUserDefaultLocaleName(t.r19, *i${NSIS_MAX_STRLEN})'
   StrCmp $R9 "zh-cn" coincide 0
-  StrCmp $R9 "zh-tw" 0 part
+  StrCmp $R9 "zh-tw" coincide 0
+  StrCmp $R9 "pt-br" 0 part
   coincide:
   System::Call 'User32::CharLower(t r19 r19)*i${NSIS_MAX_STRLEN}'
   ${StrRep} $lng_usr "$R9" "-" "_"
diff --git a/nsis/lang/README.txt b/nsis/lang/README.txt
index 07899cb..0340c30 100644
--- a/nsis/lang/README.txt
+++ b/nsis/lang/README.txt
@@ -18,6 +18,13 @@
  drop-down lists on the .vimrc page - 55 characters.
 Characters in this case mean characters of the English alphabet.
 
+Once the message translation file is ready, it must be included in the
+"gvim.nsi" file.
+Find the line "# Include support for other languages:" in the file "gvim.nsi"
+and specify the name of the file with your translation below the line
+!if ${HAVE_MULTI_LANG}, similar to the entries already there. File names are
+specified in alphabetical order.
+
 If you do not yet have a translated "LICENSE" file and/or a main "README.txt"
 file, set the following values:
 
@@ -32,3 +39,25 @@
 Translation files should be located in the "lang" subdirectory of the root
 directory. The name of the files is as follows: "README.xx.txt", where xx is the
 language code according to ISO639.
+
+
+There are two ways to test the installer in different languages:
+
+1. Find and uncomment the "!define MUI_LANGDLL_ALWAYSSHOW" line in the
+   "gvim.nsi" file and rebuild the installer.
+   Now every time you run it, you will see a dialog box with the possibility to
+   select the language of the installer.
+
+2. If the Vim editor is already installed in your system, delete the
+   "Installer Language" parameter in the Windows registry under
+   "HKEY_CURRENT_USER\Software\Vim".
+   Or you can create a file "NoLangInstallerVim.reg" with the following content:
+
+	Windows Registry Editor Version 5.00
+
+	[HKEY_CURRENT_USER\Software\Vim]
+	"Installer Language"=-
+
+   and apply it by double-clicking on it.
+   After these steps, when you start the installer, a window with the installer
+   language selection will also be displayed.