Didn´t take as long as expected, here ya go…
Maniac Mansion initial review in german Happy Computer 10/87
Confusingly the box on the far left mentions the release date of the german version to be estimated late september early october but not what year. Considering that article is in fact FROM the month of october I guess they meant the following year. Seem it came much earlier than expected because:
Earliest mention of the german version I found in ASM 01/88
Zak McKracken initial review in german Happy Computer 09/88
Earliest mention of german Version of Zak of the Amiga Port (with screenshot) from Powerplay 02/89
And if you´re curious about the interview they mention at the end of the first Maniac Mansion article you can find that here