Just in luck, I had the same problem - although I know and read Japanese... hehe... I prefer English.
1. Eject and remove any disc inside the Xbox console
2. Make sure Xbox controller is in port 1, then turn on the console (without a disc)
3. You'll see a screen, go down all the way to Settings and hit select button
4. Next screen you'll see should say Language - select that option
5. Now you're back to selecting a language of your choice.
Hope this helps
Edit If the above steps doesn't work that way, you might want to try turning off the Xbox and then turn it back on and follow step 3 and down.