patch 8.2.1544: cannot translate messages in a Vim script

Problem:    Cannot translate messages in a Vim script.
Solution:   Add gettext().  Try it out for a few messages in the options
            window.
diff --git a/runtime/doc/usr_41.txt b/runtime/doc/usr_41.txt
index 10e53ba..81474c7 100644
--- a/runtime/doc/usr_41.txt
+++ b/runtime/doc/usr_41.txt
@@ -628,6 +628,7 @@
 	execute()		execute an Ex command and get the output
 	win_execute()		like execute() but in a specified window
 	trim()			trim characters from a string
+	gettext()		lookup message translation
 
 List manipulation:					*list-functions*
 	get()			get an item without error for wrong index