As-Salamu alaykum wa rahmatullahi wa barakatu, I live in a small town in Germany and the only Masjid we have is DITIB. DITIB is very turkish culture oriented and they even sometimes do Bidd'ah out in the open. Am I still obligated to pray at that Masjid since there aren't any other ones.

Praying behind the people of bid'ah is allowed. In regards to Jumu'ah, yes, it is mandatory upon you to pray in the masjid. Just because some people, or sometimes they, do a certain bid'ah, that does not mean you have to abandon the masjid. The only time we would say you have to be careful, or perhaps pray in jama'ah and not in the masjid, is if you are going to get influenced by them and dragged into their bid'ahs. In that case, you have to be careful. But even then, we say do not mingle with them. Just pray your salah and leave, because you do not want to abandon salah in the masjid.