Multiple language posting is not supported due to Facebook API limitations.
However, Facebook attempts to translate posts into the local language of the viewer. A user can turn on multi-language translations and even select the languages they don’t want translated.
You can turn off automatic Facebook translations of posts by going to facebook.com:
Please see here Facebook Multiple Languages for more info.
If you do want to create posting in multiple languages, you can use the Translate Post API endpoint.
You may either then sent to posts to the same Facebook page, which might be confusing for your audience, or create a new Facebook page for each language.