By default, the Facebook app for Android will run in the language option set on your device. However, if you'd like to use a different language on the application, you can adjust your language settings in just a few simple steps. Here's how to do so.
Change Language Settings on the Facebook App
Open the Facebook app and tap the Menu option. Then, scroll to Help and Settings.
Next, select App Settings > General Settings:
Tap the Language option, and then make your selection: