The flight attendant control panel (visible next to Gaby's jump seat during the emergency landing scene) is entirely in French. "Landshut", the aircraft involved in the hijacking, was delivered brand-new to Lufthansa and should have had a control panel either in English, in German or in both languages.
The cars of Schleyer's convoy are not depicted 100% correctly - Schleyer's real S-Class W116 Mercedes was NOT a Model 450 SEL 6.9 ("just" a standard 450 SEL), and the W114 /8 Mercedes of his bodyguards is shown as being a Series 1 model (in reality it was a Series 2 280 E).