Germany doesn't allow dual citizenship either, unless you acquire dual citizenship at birth (perhaps you were born in the US but your mother is German). In all

Germany doesn't allow dual citizenship either, unless you acquire dual citizenship at birth (perhaps you were born in the US but your mother is German). In all other cases one either loses their German citizenship (or surrenders their foreign citizenship) immediately upon acquiring the other citizenship. If you are under 18, you get to wait until you turn 18 to make your choice (in some cases until 23). After some research it turns out that Germany allows people to acquire a foreign citizenship without losing their German citizenship in special circumstances. You need their explicit permission before beginning the citizenship process of another country. The application is free form. I just went through this a few months ago and Germany approved my request with no issues. Soon I'll be a German and US citizen.