Our company has a support site with forums and we do exactly what you indicate. We use google translate to move from one language to another. You have to pay google (I think it is $20 per million characters). We examine the user's locale information to present posts in their language and to ascertain the language when the user posts. And if that is not sufficient (user's sometimes don't have the locale set to their language), we have a set of flags at the top of the forums that the user can click to quickly translate to the language represented by the flag.
Google translate isn't perfect, but it has gotten much better as time goes by.
So the real question is how can one customize Q2A to provide the same feature. Is there some event one can intercept when a post comes in so the post can be tagged with, say the user's locale information?