I don't spend much time on Facebook, and I'm sad to say, even my Facebook page is not very active. Also, I'm not a social media guru, so I missed the announcement and no doubt lengthy discussions about page posts in multiple languages.
As a Croatian, who lives in Germany, but posts in English, I find this option awesome. Now I can make posts in both English and Croatian ... maybe even German, when my German gets much, much better.
So, here's how to turn it on.
1. Go to your page -> Settings
Sure you can find this, it's in the bottom right corner, next to "Help".
2. Simply turn on the option "Post in Multiple Languages"
There's also a Facebook explanation next to it, if you simply hover over the question mark.
3. Make a post
If you simply save changes and go to your page, you'll be given a option to post in multiple languages.
Note that Facebook will automatically suggest a translation of your post to a language of your choice. While it is certainly good to offer a translation, this option also enables you to write different content for a different language.
For example, in the following post, non-Croatian audience needs to know what is going on first, and then a comment, while Croatian audience knows very well what is going on and is only interested in a commentary.
BTW, try not to have totally different posts in different languages, as there also exists something called Audience Optimization and it's probably better suited for these scenarios.
Here's how posting in Croatian and English looks like:
Pretty cool, huh? They know what they're doing.