We agree...apart from the above-said, we have another MAJOR concern with this idea.
As a mod developer, if one of our client posts a message on a russian forum, we will probably miss it and it will lead to unsatisfied client and could eventually result in a bad review. To make things worse, do you want us to montior all these forums - russian, chinese, german, italian etc etc.
Just provide standard translation buttons on top of the english forum, so that they can just click and read the topics see more in their own language. We have never seen this idea of creating totally separate forum for different languages, please revisit the idea !!!