In The Canon:-Edit
Überwald is Terry Pratchett's trope for all things Germanic: specifically the Discworld Germany, but with aspects of Switzerland and Austria. This is the Germany of the late middle ages,all deep forests, superstitious natives, minor members of the nobilty pursuing pioneering surgery assisted by servants called Igor, vampires, werewolves and oddly, banshees.
In later books in the series, the later, more warlike, Prussian and Austrian martial tradition is moved on to Borogravia and Zlobenia. It is also indicated that, confusingly, Überwald stretches out beyond a "Germany" to encompass aspects of what we would think of as Poland, Romania, Czechoslovakia and Russia.
In the Pessimal Discworld:
I prefer to think of Überwald as being only Germany, with Bavaria perhaps dominating, and an overtone of Switzerland (Terry's invention of the Cuckoo-Clock-Building Bird of Überwald). Borogravia I see as the crumbling Austro-Hungarian Empire that collapsed completely during WW1 but still tried to fight on.
The Cuckoo Clock was invented in Augsburg, Germany.