This package allows Facebook to be translated into any language.

It is a fork of the secwepemc-facebook project which was created by
Neskie Manuel to translate Facebook into his language of Secwepemctsín.
I’ve brought Neskie’s script up-to-date so it works with Facebook’s new design,
and generalized it to work with any language.

Here are installation instructions

If your language is not yet available, it’s very easy to do a translation.
You just need to translate these words and phrases

If you’ve translated software before and you’re familiar with PO files,
I can provide you with an empty PO file into which you can place your
translations.

Once I have your translations, I’ll build a “Greasemonkey script” that you can
install in your browser, and then you should see Facebook in your language.

Excerpt from Neskie’s original README:
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A Greasemonkey Userscript to alter Facebook to display words
in Secwepemctsin.

Greasemonkey scripts allow you to alter web pages in many different ways. We
are altering the website so that words in Facebook are in Secwepemctsin. How
do you say “What are you planning?” in Secwepemctsín or how do you say “News
Feed”? I’m still looking for words to translate. Some words will be hard like
“Privacy” or “Contributor”. When we get all of the Facebook interface
translated, Facebook will be another place we can be immersed in the language.

It would be good to be able to use the official Facebook Translations App, but Secwepemctsín isn’t listed. Until then, we can use this script.

…

Enjoy Facebook in Secwepemctsín. Also check out First Voices and Secwepemctsnem for more language resources. There is also Land of the Shuswap.