I'd expand on that idea to suggest some sort of string-table text file based means of supporting multiple languages in osu! Actual graphics are necessary for the buttons though (I always use Ouendan 2.7 because I get my menus in 日本語！) So custom skins for those extra languages would be essential.
As far as song titles are concerned, we currently have a problem where Japanese titles must be printed in romaji only. Ideally, people would be able to put multiple language strings into the beatmaps they create, so that if a user had their Osu! set to display a certain foreign language, and a matching foreign language string/title were available in that file, it would show that in the menu. The same in reverse -> People who have selected English as their language would see a romaji or English title. The "default" language title should probably stick to 7-bit ASCII (for compatibility), but any other language UTF-8. That way..
well, I'm rambling, but you get the idea. I'm a Japanese nut, so I'd enjoy such a feature.
