I used to not understand most of what they said in English, but as I got better I started understanding more and more, though still there are certain artists that I don't understand everything, especially when it's rap xD So yeah, if I don't understand I just make noises with my mouth hahahaha
Rammstein's "Du Hast" was really popular when I was a teenager. It was just "known" that he was saying "you hate me" but then I found out that he's actually saying "you have me" and the song is way different than I thought. Whoops!
I do that when I'm listening to songs in French or English (when they speak too fast). It's funny, but it's also a way of motivating yourself to learn a new language. So, after listening to the songs, I usually look for the lyrics to understand what the singer is saying. And I learn a lot with that.
I like songs in Spanish and the songs that I sing are so nasty but I didn't know that until before 2 months. Something like me gusto todo de ti, tu tan bonita el no te da, me lo paro el taxi, tu y yo bailando hacemos el amor con ropa. Specifically the last song got me invited to a Mexican party :P
But they are just one night stand pick up lines. I dont sing them anywhere now xD xD