It would be difficult to find the original opening title sequence, but most promotional material seem to use "Monty Python's Das Leben des Brian."

I can't follow that since most sources use the IMHO correct German title, just „Das Leben des Brian“. When "Monty Python's" (or "Monty Pythons") is used it is just an additional info but not part of the title. It's also a question why it is "Monty Pythons - Das Leben des Brian", with dash, here. Not only Wikipedia but also https://www.synchronkartei.de/film/1908 just uses "Das Leben des Brian". The opening title sequence (on my DVD) uses the English title ("Life of Brian").

If I look to the official (?) poster, I see the title in quotes (and Monty Python’s is just used for crediting the troupe, but not part of the title).

https://www.filmposter-archiv.de/filmplakat.php?id=24599