
Russians wearing German Winter uniforms....also summer uniforms too. Just read one of the books were the Authour runs up to 3 "Germans" in MP uniforms only to be gunned down by them. One of his friends is killed and the 3 Russians are killed by another German......
Since it was hard to distinguish friend or foe in winter whites the Germans put a Red band around one arm. If you find a picture of Germans in winter whites you will see them with a dark strip around one arm.
As for the Brits with German speaking soldiers.....there is a movie out on this. Older one where the main character gets gunned down by a friendly soldier right at the end of the movie. Can't think of the name right away here.
Yes, you are correct about soldiers being executed if caught in enemy uniforms however, all the Armies did it. Even Geneva Convention does not regonise Partisans/Guerilla units.