Even with my in-progress wikilink fix (bug 43498), messages like https://www.mediawiki.org/w/index.php?title=Special%3AAllMessages&prefix=newarticletext&filter=all&lang=en&limit=50 don't work. The original message source is:
You have followed a link to a page that does not exist yet. To create the page, start typing in the box below (see the [[{{MediaWiki:Helppage}}|help page]] for more info). If you are here by mistake, click your browser's '''back''' button.
It doesn't yet have any support for recognizing the {{MediaWiki:message}} construct
Version: 1.21.x
Severity: enhancement
See Also:
https://bugzilla.wikimedia.org/show_bug.cgi?id=43499