1. Go to Control Panel.
2. Click ‘Change date, time, or number formats’
3. As the Region dialog appears, choose Administrative and click Change system locale.
4. Select Japanese locale and click OK.
5. Restart to make changes effective.
You can also use Locale Emulator.
1. Download and install from here: http://pooi.moe/Locale-Emulator/
2. Whenever opening a game, right click on it and select ‘Run in Japanese’.