Corrected entry: The airplane shown taking the young Maria and her husband from Vienna to Cologne is a Douglas DC-3, an American product which would not have been used in Germany at that time. The Fuhrer would not have permitted it! German airlines would have used the trimotor Ju 52.
During the arbitration supposedly set in Austria, we can see at first glance a British Coat of Arms in the top of the wall of that beautiful room. No official Austrian building would display a foreign coat of arms - the scene was filmed in Britain.