Before going back to California from Berlin, I went to Glasgow to visit my friend who is studying in the University of Glasgow. It was also Halloween so we went out to some bars and club. While waiting in line, I couldn't understand what people were talking so I turned back and asked a guy "What language are you speaking?". "English." he replied. "Why couldn't I understand at all?" "We use a lot of slangs."
I thought they were talking in Scottish.