Japanese, Korean, possibly even Chinese.
Japanese for the obvious reason that I’d be able to make myself understandable in Japan, might even possibly live there. (Depends on whether the reading part was also incuded.)
Korean because,.. I’d be able to watch all of the drama when it comes out, insted of having to look at poor translations or just waiting for the English subtitles.
Chinese, because.. China is becoming a larger economic force in our small world. It would be good to learn it now so that we can communicate with a lot of people whom we usually would not be talking to