For pre-war German stereotypes I really like the Schlegel sisters in "Howards End" (from 1910) who are half-German so more cultured than the English and understand Beethoven. I think their father was a German Professor. Howards End is one of those books which is extremely well-written and literary but kind of ridiculous underneath, but some of that might be because Forster is playing off outdated archetypes.

There was an episode of the radio series "John Finnemore's Double Acts" last autumn with a German character which I thought was v well-written. Her being German is part of the plot -- she wants to improve her English so she can read fanfiction and the episode is a conversation lesson she has with a runaway English teenager who's trying to pass herself off as a qualified teacher -- but most of her characterisation isn't about her Germanness. I liked it because John Finnemore clearly speaks at least some German and the linguistic jokes aren't based on Elke being bad at English but on Lorna being so bad at teaching it that she keeps making Elke's English worse. Anyway, I recommend it if you're looking for good German characters in British media (it's no. 5 on here http://fourble.co.uk/podcast/johnfinnemoresdoubleacts)