I think Prochnow was born in Berlin and lived for most of his life in northern Germany. Perhaps he put on an Austrian accent for the film -- which would make sense, because the Austrians and Bavarians are considered rather backwards rural folk by the Prussians and their ilk. It really is the same as the attitude towards rural Southerners by New England liberals. It would make sense for a brave and good commander to be a simple country boy, in contrast to the political officer and the career Nazis . . . .
But if he had an Austrian accent, I would never know it, because that just sounds NORMAL to me!!!!!