Several posters have said about not being able to translate everything into all minority languages. Thing is, if this is indeed the German School, the question is about providing important info in English, as promised, or only in German, as seems to be happening. Providing translations into the local language i.e. English is a different thing to providing translations into one or several 'minority' languages IMO. I would expect any school in England to provide English language info - even foreign language schools. Anything else would be exclusionary to any non-German speaking parents and kind of implies that the school only really wants all-German families, and will do nothing to include non-German spouses.
I happen to know that this particular school has had exactly this reputation for a while. That it is basically ideal for (all-) German families, families that have more or less temporarily moved away from Germany but whose kids have been born in Germany, perhaps begun their schooling in Germany, and might very well return to Germany at some point.
That in contrast, local bi-national families choosing the school to reinforce the German whilst essentially being British families with a German mum or dad have always felt a bit sidelined. Also Austrian and Swiss families.
From all the points you list, OP, I suppose some are indeed down to different cultural expectations, but others have nothing to do with culture but are simply signs of a badly run school. Things like not being able to reach a teacher, not getting calls returned, ineffective dealing with bullying, you can encounter these things at any badly run English state school, they have nothing to do with 'culture'.
Usually if at an unsatisfactory school you would walk away - but there are some things that only this school can offer you (perhaps that's why they can afford to be the way they are) so you have to sit down with your husband, explain exactly what the problems are and what effects it is having on you and your child, and decide together how to move forward.
Perhaps this will mean leaving all communications with the school to your husband, and intentionally finding ways to include you and your child more into the local English community.
Perhaps it will mean leaving the school and figuring out other ways to support your child's German language and culture.