Thread:Support/List of all system messages of translatewiki.net cannot be displayed/reply

Yes, it's been broken for several months or perhaps some years. There are just too many messages on this wiki for Special:AllMessages' code to deal with, I've been told it's not reasonably feasible to fix it. You can always use it on the wikis where you see/use the messages/extensions, though: what would you like to use it for? Maybe there's an alternative here.