What is fascinating is that the all people you encounter will speak a different combination of languages, depending on where you are in the city, or where they come from.
In Hamra, you'll hear Arabic, and English the closer you get to AUB (the American University of Beirut)
I Ashrafieh, you'll hear Arabic and French, and English the closer you get to ABC (the mall).
What I love about the Lebanese is that they use all the languages they know interchangeably when speaking, because the person they are talking to also understands perfectly well, so there is no need to make an effort to stick to one. And the more languages they know the more they'll use.
So if you have the good fortune of knowing one or maybe 2 of the languages they speak, conversations sound like this:
At a party 2 girlfriends are talking, "Yesterday, blah, blah, blah, blah, black leather, blah, blah, blah, blah, I told him, blah, blah, blah, blah, I like it very much." (turns out they were talking about a new car)
At the office, "Hi dear, blah, blah, blah, no way, blah, blah, blah OK, blah blah, khalas. Thank you. Yalla bye"
At the Yoga studio. "Hi!!! Blah blah blah?" Very cute! Blah blah blah blah blah in ABC, blah blah blah blah, half price."
There are some words like Mabrouk! (Congratulations), Sukran (Thank you) or Marhaba (Hi!) that you'll start using as a foreigner, as a way to integrate yourself and not sound absolutely clueless.
And inevitably all Lebanese will sprinkle their conversations with the following 3 absolutely transferable words, no matter what language they are speaking in or who they are talking to: "Yalla" (very similar to the Spanish "Vamos"), Ya3ni (Very similar to the English "I mean") and Khalas (that can mean "That's it", or "stop", or "finished", or "allow me").
So... shukran for reading. A bientot. Yalla, bye