I speak Dutch, German and English. And to a very, very small degree... some french. I once had French 1 year in high school. Apart from that that... I speak the local dialect, which is kinda like German. If I'd speak that in Germany, most people wouldn't have a lot of trouble understanding what I'm saying. It has occured that when I was in Germany, locals didn't believe I wasn't native... that was kinda funny. I had to show em my ID to prove I wasn't German.
More intested in where words come from or how a language is, like it is, than I am for learning new languages though. However, I've dabbled a bit in Russian, Japanese, Spanish, Norwegian and Italian. I also looked around a bit in some of the fictional languages like Nadsat, Tengwar & Klingon. Oh, and Polari, I spend some time in the past months on reading up on that. I think for most part I could understand/read it, though not really speak it.
I do enjoy reading up on slang and contemporary "urban" language. Sometimes it's a funny play on words and I do enjoy wordplay a lot.
Cockney rhyming slang is kinda odd to me though. It has nothing to do with actually understanding the language but rather than learning idiom cause both parties should, if by means of understanding, be aware of the reference one makes. But it's funny to read and listen to.
The reason I rarely learn something new is because it lacks practical application. Some people, even in Holland, speak terrible Dutch, and they're native. So I don't think that learning Klingon to have a convo at the employment center is gonna help me there.