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/repeat.txt b/runtime/doc/repeat.txt
index e95b6a1..0bfb117 100644
--- a/runtime/doc/repeat.txt
+++ b/runtime/doc/repeat.txt
@@ -1,4 +1,4 @@
-*repeat.txt*    For Vim version 9.1.  Last change: 2023 May 26
+*repeat.txt*    For Vim version 9.1.  Last change: 2024 Jun 20
 
 
 		  VIM REFERENCE MANUAL    by Bram Moolenaar
@@ -735,6 +735,10 @@
    start/foobar/autoload/foo.vim	" loaded when foo command used
    start/foobar/doc/foo.txt		" help for foo.vim
    start/foobar/doc/tags		" help tags
+   start/foobar/lang/<lang_id>/LC_MESSAGES/foo.po
+					" messages for the plugin in the
+					" <lang_id> language.  These files are
+					" optional.
    opt/fooextra/plugin/extra.vim	" optional plugin, defines commands
    opt/fooextra/autoload/extra.vim	" loaded when extra command used
    opt/fooextra/doc/extra.txt		" help for extra.vim
@@ -762,6 +766,35 @@
 	:helptags path/start/foobar/doc
 	:helptags path/opt/fooextra/doc
 
+The messages that are in the lang/<lang_id>/LC_MESSAGES/foo.po file need to be
+translated to a format that the |gettext()| function understands by running the
+msgfmt program. This will result in a lang/<lang_id>/LC_MESSAGES/foo.mo
+file. See |multilang| on how to specify languages.
+
+In your plugin, you need to call the |bindtextdomain()| function as follows.
+This assumes that the directory structure is as above: >
+	:call bindtextdomain("foo", fnamemodify(expand("<script>"), ':p:h')
+	 .. '/../lang/')
+<
+You only need to do this once. After this call, you can use: >
+	:echo gettext("Hello", "foo")
+<
+to get the text "Hello" translated to the user's preferred language (if the
+plugin messages have been translated to this language).
+
+To create the foo.po file, you need to create a foo.pot file first. The
+entries in this file need to be translated to the language(s) you want to be
+supported by your plugin.
+
+To create the foo.pot file, run the following command: >
+	cd ~/.vim/pack/start/foobar
+	make -f ~/src/vim/src/po/Makefile PACKAGE=foo \
+	PO_BASEDIR=~/src/vim/src/po PO_INPUTLIST= \
+	PO_VIM_JSLIST="plugin__foo.js plugin__bar.js \
+	autoload__foo.js" \
+	PO_VIM_INPUTLIST="plugin/foo.vim plugin/bar.vim autoload/foo.vim" \
+	foo.pot
+<
 
 Dependencies between plugins ~
 							*packload-two-steps*