What is the experience of being a native English speaker like in Germany?

Hey guys, I'm planning to study abroad in Germany but worried about language barrier I'm already well rested in French, Russian and German, discluding English, but still want to know how people treat you when they hear you speaking only English. I've heard that people in Germany tend to be harsh on tourists who don't speak German, is this true or no? Also does anybody know what's the experience in Vienna Austria like?. The German dialect is the same as Germany isn't it?. Thanks!