Step 3 : In the Choose Language dialog box, click the arrow to display a list of languages that Facebook supports.
How to change Facebook language on computer Picture 3
Click the arrow to select the display language on Facebook
Step 4: Select the language you want to change, here we are using Facebook in English so we will change to Vietnamese.
How to change Facebook language on computer Picture 4
Select Vietnamese language for Facebook to display in Vietnamese
Step 5: Click Save Changes to save the Facebook language settings you just selected
How to change Facebook language on computer Picture 5
So, you have successfully changed the language on Facebook. You can change it back or change it to any language you like in the same way.
Good luck!