The title says it all. I just recently transferred all my files on to a new account. The first thing that I noticed is that the Start screen wasn't 100% in English. So I looked in my language thingy, everything is in English. I have no idea what's going on
Open Control Panel/language and make sure Japanese is not listed as the primary language - use Move down to prioritise. Also check Advanced Options for your preferences.
Curious! You have logged off and back on after making the change? If that hasn't worked, perhaps you should try removing and re-adding the language(s) you need.
Edit:
Odd enough. I just fiddled around with the Language under Control Panel and it changed to English