[Sangetsu]

Most graduate students I know have a working knowledge of English, and I have yet to meet a Japanese professor whom I haven't been able to communicate with in English. That's not to say that there aren't any, but you should be able to get along fine using English.

It wouldn't hurt to study a little Japanese before coming over, but you only need enough to introduce yourself, and for shopping. For a stay of only a few months it's not worth the trouble to learn any more. You would need at least a couple of years of serious Japanese study to acquire even basic conversational skills.