Three Hurrahs For Germany!
It can be taken by any country with a primary culture of North German or South German. The requirement is to own or have sphered all provinces with German cores. Luxembourg and Austria is however optional. It is also a requirement that the forming nation has 45 prestige.
Note that despite Ashkenazi technically is a Germanic culture, Israel is unable to form Germany and Ashkenazi will not be an accepted culture in Germany.