Usually, Facebook displays English as the default language on your profile page, though it may change the language automatically based on your region as well. You can, however, change the language displayed on your Facebook profile page by configuring the General Account Settings screen. Since a language change affects all other pages and settings screens besides your profile page, do not change to a language that you do not know.
General Account Settings Screen
While signed into your Facebook account, click the down-arrow shaped button at the top of the screen. On the context menu that shows up, click “Settings.” Click the “General” side-tab, then click “Edit” next to the Language option. Next, click the pull-down menu next to Choose Primary, then select your preferred language from the list shown. Finally, click “Save Changes” to apply the language change.
If you accidentally apply the wrong language, don't click away from the General Account Settings screen -- use the language selection menu to immediately select the correct language. All language names are displayed in their native characters, so you should have no trouble identifying the correct language.
Any Facebook Page
Alternately, you can also change your language via any Facebook page. To do so, scroll down to the very bottom of a page and click your language. On the Select Your Language pop-up box that shows up, select your preferred language and click “Okay.”