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.

src/po/tojavascript.vim

@@ -0,0 +1,18 @@
+" Invoked with the name "vim.pot" and a list of Vim script names.
+" Converts them to a .js file, stripping comments, so that xgettext works.
+" Javascript is used because, like Vim, it accepts both single and double
+" quoted strings.
+
+set shortmess+=A
+
+for name in argv()[1:]
+  exe 'edit ' .. fnameescape(name)
+
+  " Strip comments
+  g/^\s*"/s/.*//
+
+  " Write as .js file, xgettext recognizes them
+  exe 'w! ' .. fnamemodify(name, ":t:r") .. ".js"
+endfor
+
+quit