Sites like Rising Gods often host "patched" German clients specifically for the DACH community.
Oft ist der Basis-Download auf Englisch (enUS). Um das Spiel komplett auf Deutsch zu erleben, hast du zwei Möglichkeiten:
⚠️ This client is for private server use or local testing. You need an existing WoW license from Blizzard for official servers.
Downloading a "WoW WotLK 3.3.5a Deutsch" client provides several helpful features for players who want to experience the peak of the Wrath of the Lich King expansion in their native language. Key Benefits of the 3.3.5a German Client Complete Localization
Computer Science, Information & General Works 
Philosophy & Psychology 
Religion 
Social Sciences 
Language 
Pure Science 
Applied Sciences 
Art & Recreation 
Literature 
History & Geography