I tried to play with the language for the forum and now my entire site is fcked up. The lang keys and translations are there but somehow they're not integrated anymore. Deano did explain it to me though.
My advice is forget about the forum, and by uninstalling the forum you may end up with some database error and likely eff up the whole site, too.
so good luck.
P.s I bought the combo language translation package from 2 vendors here and they were willing to help me with this problem but I just don't have time now to look into this. so if you're using 2nd language on your site I'd recommend you to buy the Master Language String editor, it's friendly, easy to use the and the vendor will likely help you translating the forum language file.