How to change the app's interface language in Windows 8?
You can change the display language of any app by putting the preferred one to the top of your system languages list (keyboard layouts list).
To open the keyboard languages list, go to PC Settings (Settings -> Change PC settings) -> Time and language -> Language and region -> Languages section.
Move the language that you need to the beginning of the list. You can do it by clicking the language and then clicking the button "Set as primary".