I've been working on this particular problem for the past few days, and even designed a new font for MP, but unfortunately have run into a bit of a showstopper in the framework I'm using, so it'll have to wait until that's fixed. This is a known issue, though, and I'd like to get it fixed;  not sure about Japanese support, as I feel like that would require a lot of extra work. Maybe I'll revisit the idea once enough people express interest in writing in Japanese from within the software.