That interpretation makes sense to me. When I have known people to use the wrong pronoun because of language difficulty, they are usually about as embarrassed about that as they would be about having any other language mistake pointed out to them--so it varies by person. But Breq is both trying to be polite, and trying to ingratiate herself with non-Radchaai people. Maybe "ingratiate" is too strong, but she does try to seem trustworthy and knowledgeable when interacting with other cultures, inasmuch as she is able. Plus, in her conversations with Strigan, which I think is where she is most annoyed to have gotten someone's gender wrong, Breq didn't especially want to be seen as Radchaai and that was a giveaway.

Regarding the German translation, I assumed that when the translator checked on someone's gender he was checking on someone non-Radchaai. There are a few people like that in the books who don't get gender pronouns because they aren't referred to in their own language in the third person, but if they were speaking of themselves and needed to inflect an adjective or something then it would reveal what grammatical gender they use for themselves. Which seems like a good time to consult the author--she doesn't get to dictate interpretation, but she does get to decide about the words that make up the text.