Windows 8/10 Click Start, then Control Panel. Click "Clock And Region" and pick Region. Click the Administrative tab. Under the Language for non-Unicode programs section, click Change system locale and select Japanese. Click Apply.
Windows 7 Click Start, then Control Panel. Click "Clock, Language and Region" and pick Region and Language. Click the Administrative tab. Under the Language for non-Unicode programs section, click Change system locale and select Japanese. Click Apply.
Windows Vista Click Start, then Control Panel. Click "Clock, Language and Region" and pick Regional and Language Options. Click the Administrative tab. Under the Language for non-Unicode programs section, click Change system locale and select Japanese. Click Apply.
Windows XP Click Start, then Control Panel. Click "Region and Language Options" and pick Region and Language. Click the Administrative tab. Under the Language for non-Unicode programs section, click Change system locale and select Japanese. Click Apply.
It should be noted that it is not a perfect alternative as many games will experience text errors, crashing, or just plain not work while run using Locale Emulators, as opposed to properly setting your system to Japanese locale. So, while it may seem convenient at first, it is not a viable alternative for playing more than several games. You have been warned.