I liked this topic from Long and Short Reviews. There was a time when I was learning every language I could. I've always been good at languages, and my degrees are in linguistics, so I love to pull a new language apart and see what makes it work. However, I admit right now I'm not learning any.
In the past I've learned French, Italian, German and Spanish in the traditional way, and also attempted Polish, Portuguese, Dutch and Norwegian by way of Duolingo and Babbel. I may return to Norwegian and Portuguese at some point - Polish gave me a headache with all the inflections, but Norwegian and Portuguese were fun. Which led to one very interesting moment a few years ago.
I was getting a tattoo done - my very first specially-designed back piece, done by a Brazilian tattoo artist who was sharing a studio with a Brazilian-Japanese artist. I was on that table for about six hours, including the time my tattooist stopped for his lunch break, and the whole time he and his coworker were talking about me in a mixture of Portuguese and Spanish. I wasn't fluent enough to pick it all up, but I definitely caught a few off-colour remarks about my body, along with "Are you sure she can't understand us?"
Sadly I also wasn't fluent enough to answer them back in either language, otherwise I would have done. And at least it was a decent tattoo.
So which languages are you learning?