I don't know exactly what the situation is in other countries/languages but, at least in Portugal (where I'm from), people that don't speak english are usually not the type of people that search for online forums or uses the internet that intensively. With this I mean that i think it would be pointless to have sub-fora (yes, portuguese is a latin language ) for different languages, as people that can't understand english would also be the people less likely to search the web for answer to some particular question or find this forum anyway.
Besides, having the forum in several languages seems really weird and I don't think it would work out so well.
I agree that translating the wiki to these languages would be much more productive and produce much less clutter than having sub-fora.

my 2 cents (not worth much more than that, really)