I wrote back in 2016 a guide to help if your language choice got changed on Facebook.
Read here: How To Change Facebook Language Back To English
I don’t know if it’s still a problem but Facebook has gone through some noticeable changes, so here is an updated version. Sign into your account.
Click on the triangle.
Then click on Settings & Privacy. It’s the gear symbol beside it.
Then click on the Language option, the last item on the menu. It currently has a globe symbol beside it.
This will take you to Language and Region Settings.
In the top section on the right-hand side of the page, click on the word Edit (or whatever language it’s in). It’s blue in colour.
Then in the Facebook language section, click on your language choice in the drop-down menu.
Then click on the first blue button to Save Changes.
So, has anybody had a language change issue since the new look came in? Let us know in the comments.