Log off Windows then log on again so that the update takes effect.
If Japanese was not in the drop-down list, please follow these instructions: Restart PC so that the update takes effect. ( OPTION 3 ) How can I set Windows 7 to Japan/Japanese?
Click on Add a Language under Clock, Language, and Region.Press the Windows key, type ‘control panel’ and open the Control Panel.For Windows 8.1 and earlier versions of Windows 10: