To give specific examples:
I have a friend originally from Japan, now living in London. She often posts in Japanese for her friends back home.
I have a friend originally from Romania, now living in the Bay Area. She often posts in Romanian for her family.
Both of these people also post a lot in English for the benefit of their English-speaking friends, such as myself.
I have only 24 FB friends, but some are in Sri Lanka, Philippines, Indonesia, Ukraine, Norway, Mexico, Trinidad, so I do get some.
Oh, crap, I did forget Russian. (And, oddly enough, though my family is Polish, I don’t think I’ve seen a Polish post in the last month or much at all, really.)
I can’t say for certain about the past month but my cousin’s wife is from India. She mostly posts in English, but sometimes some of the comments on her posts are in what I assume is Hindi.
I have a friend in France who usually posts in French, but he posts less than once a month.
Then there’s the guy from Nepal who posts maybe 2 or 3 times a year in what I assume is some dialect of Tibetan.
I’m on my phone so polling functionality doesn’t work.
English
Spanish - I’ve got about 2-3 friends who will commonly write something in Spanish
Korean - 1 friend who occasionally will post in this language
And one friend who occasionally posts something in Hebrew, but it’s pretty rare
They speak English in Trinidad allegedly.
Two. One lady from the Ukraine added me. Thought it might be just one of those fakes, but I checked her profile and she seemed legit–and still does. She doesn’t speak English very well at all, and I’ve never asked her why she added me.
I do occasionally have Spanish show up, due to my Mexican friend from high school. And then there is another friend from high school who seems to do a lot of globetrotting, though she doesn’t really post in other languages. It’s more that sometimes people who respond to her will get into a conversation with someone else who speaks a different language.
Still, this month, it’s just two.
Though I, like Leafan, am surprised that more than 1 is really all that common. I thought I was weird for having that one Ukrainian FB friend. Is the title skewing the results?
Now, YouTube comments–that’s another story. Those often wind up being from someone in another country, and, for some reason, YouTube displays the entire notification in their default language.
My friend there frequently writes sarcastically in local patois, and I often can’t fully understand all of it. One recent post was MEN DONT FLIKKIN LISTEN INNO!!! AH TELL HIM PEAS AN CARROT WID CORN, LOOK WHAT D CYATFISH BRING!!!
My Filipino friends write mostly in Chavacano, but sometimes in Tagalog or Visaya.
besides English:
Afrikaans
Xhosa
Zulu
French
Arabic
Japanese
Finnish
Swedish
Danish
Dutch
German
So I voted 8-11, include English and it’d be 12-15
Polish, Welsh, Swedish, Hebrew, Turkish, Latin, English. The Polish and Welsh is from the same lady, native Polish speaker, English since coming to live in the UK 40 odd years ago, degree in Welsh and Ancient Welsh, working as an archivist in Wales. One hell of a linguist.
As surprised as I am that of over 50 people responding so far, only 2 said English only, I’m just as surprised that the person from Canada is asking why other languages would show up (unless you’re confused about the question). Leaffan, is no one posting in French (or possible even Hmong).
As for my feed, the only language I see on a regular basis other than English is Swedish. I have a friend that had a couple of foreign exchange students from Sweden back in High School that I met at her wedding. They’re FB friends with me, so I get their posts, but about half of them are in Swedish and half of them are in English.
Some of them I don’t even know what language they are! 
Not “English only”, but one language. 
This, basically. You travel somewhere and make friends. Or someone else travels and you make friends with them. It’s so easy to stay in touch these days. And people who make friends easily often post frequently.
I’m surprised (as shown by my poll options) that there aren’t more people with more languages. I don’t have that many friends on Facebook; about two hundred. I know several people who have many times that (and at least one who hit the cap). And I grew up and went to college in Ohio, which doesn’t have a reputation for being very international. So I expected some people to have a lot of multilingual contacts.
English, Russian, Indonesian, Arabic, Dari and Pashtu. I can only read English and Russian, but I would feel bad deleting former colleagues who post in the other languages. If it’s a picture of a baby or a wedding, I just hit like.
Geez, of all the possible languages one can choose, she went with the two that look like you are just mashing the keyboard with your palm repeatedly 
Yeah. I do see French posts occasionally. But even my French friends usually post in English.
Sorry. I had a brain fart and didn’t think about the post before responding.
And, as I read French reasonably well, I didn’t even think of it as a second language.
Aluminum pots are taking their toll apparently.
Sent from my XT1635-02 using Tapatalk
But you can have endless fun with the translate feature 
In seriousness it’s usually enough to get the gist or if not to know what questions to ask. One of the Hebrew accounts linked to a fascinating article about the friend’s grandfather. I used google translate on that and, when I queried a couple of the more bizarre bits, my friend, who is a translator did the whole article and posted it.
English
Urdu
Chinese
French
Finnish
Catalan
Vietnamese
These seven I’m sure of. I haven’t gone back a month’s posting to check but there could easily be in addition:
Thai
Nepalese
Sinhala
Several Indian languages
Arabic
Spanish
Japanese
Dutch
German
English
Portuguese
Icelandic
English
French
Spanish
Amharic
Wolof
I don’t speak or read Amharic, but I enjoy Ethiopian music, so I get stuff from African video channels. The Amharic script is in wide use.
The Wolof is from a Senegalese friend.