Austria and Switzerland

German has three standard forms: the German of Germany, Austrian German, and Swiss Standard German. All three are correct, and each has its own words and pronunciation. If you learn German in Germany, you'll be understood everywhere — but knowing the local words makes a big difference in Vienna or Zurich.

In German-speaking Switzerland there's a second layer: in everyday life people speak Swiss German (Schweizerdeutsch), a group of dialects that can be hard even for Germans to follow. They write and read standard German, though, and will switch to it for you.