You selected the language for your phone during set up. To change it:
If you don’t see the language you want, tap 
All languages added to the list will appear on the keyboard's spacebar.
To remove a language, go to Settings > System > Languages & input > Languages, then tap 

For specific apps, you can select a language that's different than your phone's default language:
Tap the app's name and select the language to use.
Not all apps support changing languages.
If you want a keyboard for a language that isn't a display language:


Then, switch between languages on the keyboard by tapping 