Ethic veganism is a philosophical belief protected under Art. 9 ECHR and Art. 4 of the German Grundgesetz. Where the state is responsible for people’s meals, i.e. in prisons, schools or the military, it must allow and provide for sufficient vegan options, just like it accomodates other religious eating habits.
This is the basic argument of Dr. Armin Huhn and Dr. Justine Diebel at the District Court in Kempten, where the two represent a vegan prisoner against the local correctional facility.