Germany is a huge gap, noting that the Teutons are a civ very much modeled on the Teutonic Order, which was located in Eastern Europe. Even UU is typically Teutonic Knights absent in HRE.
Holy Roman Empire
Teutonic & Livonian Orders
When it comes to the Balkans and the broadly understood Eastern Europe, I invite you to the topic that I have created: absolutely definitely the last Eastern European DLC