thecoalman - 1:13 pm on May 30, 2011 (gmt 0)
If it were me doing this from scratch I wouldn't use different domains. Different language packs are available and when the user registers they have the option of choosing their own language.
From there you can apply a different theme to any forum. Templates are inherited so you could for example just alter the CSS. You would have visually different forum for each language. AFAIK there is no option out the box for applying a default language to specific forums but should be an easy modification if you can't.
Th benefit of course is you have it all under one login, the user can navigate to different forums with other languages.