My native language is English, so why is it that I can only pick up Slavic languages quickly?

I think that this is pretty strange. My native langauge is English, but I can not understand German or any other languages that are similar to English. They all sound like gibberish to me. But I can easily pick up Slavic languages. For example, my favorite movie is this Czech movie called 'Sedmikrasky', and while I was watching it for the first time, I picked up some of the things that they would say to one another. Like, "Do you mind? No, I don't". The second time watching the film, I can say complete sentences in Czech correctly and with an accent. The same goes to Russian. I also just listened to a song in Bulgarian, and after listening to it for a second time, I can repeat the chorus perfectly. But Spanish, French, German, etc. sounds weird to me.