[Logician]

I would say it may be easier to use 1 vb for your site instead of trying to merge 2 vb databases.

I recall I give this solution before but basically it's how it works:
Create 2 usergroups for each language. Set forum permissions so that each usergroup will access to the forums that is in its language. Then put a small link in the header named "Change Language" or smt. and create a one line hack which will change the usergroup of the user when clicked. So their languages and the boards they access changes either..

Just a thought..