For anyone interested:
Asteen Cathedral = Ersten Kathedrale = First Cathedral
Zweiten Cathedral = Zweiten Kathedrale = Second Cathedral
Drotten Cathedral = Dritten Kathedrale = Third Cathedral
Faiten Cathedral = Vierten Kathedrale = Fourth Cathedral
So the cathedrals are literally just numbered.
Grune Castle probably = Grüne Burg = Green Castle
Reading the names kinda hurts my brain and imo it would fit better if it was, for example, "Erste" instead of "Ersten" (same for the others) but hey,
gotta get used to it with all the other fantasy manga with pseudo/semi german/european names lol