To permanently change the Input Language, go to Start>Settings>Time and Language. Select Region and Language. At the bottom of the window, you'll see a hyperlink that says Additional Date, Time, & Regional Settings. Click that hyperlink. It will open this window:
You can click Add a Language or Change Input Methods and it will open this window:
Under the language you want, click on Options. It will open this window:
Under Windows Display Language, select this language as your display language.
You must log off and log back on for the settings to take effect.
For Microsoft Word, the display language is set under File>Options. Select Language. The display language is in the bottom half of the window:
Good luck!