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" "-" "_"