Under appearance settings, enable “Smart Quotes”.
If you are on an iPhone or iPad, and using an on screen keyboard make sure that it is a a German one.
I think hardware keyboards will pick it up from localisation.
Should you need to convert between styles of quotation marks I created a set of actions to do that in the “Quotation Marks” section of the ThoughtAsylum - Writing action group. The ones for German quotes have “High Quotes” in the name. There are actions in there for dealing with conversions between various styles of quotation marks including smart, “dumb”, guillemots, inversions, and high/low splits such as those used in Germany.
Hope that helps.