1. Go to Control Panel.
2. Click on ‘Change date, time, or number formats’
3. As the Region dialog appears, choose ‘Administrative’ and click on ‘Change system locale’.
4. Select Japanese locale and click OK.
5. Restart to make changes effective.
Using Locale Emulator.
1. Download and install it from here: http://pooi.moe/Locale-Emulator/
2. Whenever opening a game, right click on it and select ‘Run in Japanese’.
NOTE: The archive with the game must also be extracted using the emulator. Otherwise you might get a bunch of errors saying some files are missing.