Well, its not that bad if you don't speak the language. It will make things tricky if you have to communicate something important, like ask for directions on the street. But if you are just taking the bullet train up, all the station names and major signs are written in Japanese as well as the our alphabet.
Finding restaurants are not that hard, but reading the menu might be problamatic until you get to Niseko. However, there are convenience stores everywhere, and you will not starve.
Learn some basic greetings, how to say thank you, the major faux pas (don't wear your shoes in the house, don't stick your chopsticks in your rice, etc) , and you should be OK.
