I have two gaming groups in Tokyo. In one, we play a modified D&D 3.5. But it's all foreigners, and getting people to participate in a cross-lingual game seems very difficult. We've gotten a lot of 'that's interesting, sounds fun, eh, I couldn't possibly...' when talking about it to locals.

And, to be fair, out of our groups maybe one player would be proficient enough to play in Japanese. I think it would be interesting to try as a way to improve my Japanese but probably I wouldn't get much out of the game itself at my level.