Karl, there's a couple of things you can check. First, change your Profile, Account Related Settings to English and see if that fixes it. Unless they fixed the forum after your post, it is working fine for me right now. I assume you tried deleting your cookies & cache?
If it is still not fixed for you and others, it could be a forum problem, admin has to make sure /Themes/default/languages/index.english.php is there and correct, otherwise might have to do a
repair_settings (after a backup of course). Oh and if there was some recent addition to the forum, undo that first to see if it fixes it. But like I said, I'm not seeing that message so it could be your login.
cheers