patch 9.1.0509: not possible to translate Vim script messages

Problem:  not possible to translate Vim script messages
          (RestorerZ)
Solution: implement bindtextdomain() and gettext() to support Vim script
          message translations (Christ van Willegen)

fixes: #11637
closes: #12447

Signed-off-by: Christ van Willegen <cvwillegen@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/runtime/doc/usr_41.txt b/runtime/doc/usr_41.txt
index a54a991..922e80a 100644
--- a/runtime/doc/usr_41.txt
+++ b/runtime/doc/usr_41.txt
@@ -798,6 +798,7 @@
 	execute()		execute an Ex command and get the output
 	win_execute()		like execute() but in a specified window
 	trim()			trim characters from a string
+	bindtextdomain()	set message lookup translation base path
 	gettext()		lookup message translation
 
 List manipulation:					*list-functions*