Of course you don't need to know the language to just get by. You can easily just learn enough phrases to do what you want to do. However, it would make more sense to learn Japanese if you want to actually LIVE there. What's the point of going there if you aren't even going to try to learn the native language. I feel that's disrespectful to some extent. You don't have to be fluent, but you should at least try.
