The TWA 727s had a long history of being based in Southern Europe, one ran Tel Aviv-Athens-Rome as a 747 feeder for many years. Alex Frater, in his classic book about old air travel "Beyond the Blue Horizon" rode in it from Rome to Athens in 1984, and described it in detail. Both flight deck and cabin crew were from the US, the latter revolving with 747 Transatlantic duties. TWA later moved in to Berlin as a competitor on the internal German routes, just a year or two before the wall came down so a wasted investment.
Pan Am at Berlin likewise had US flight deck, they were on 3-month assignment at a time from Miami base. It was a 4-powers agreement that the crews had to be nationals of one of the Allies, but cabin crew were locally recruited. They had to have additional training to repeat all necessary commands from the flight deck in English to the pax in German. A distinctive feature of the Pan Am internal German service ("IGS") was the very short turnrounds, down to 25 minutes, and the heavy usage, 10 sectors a day or even more.
The GDR controllers on the corridor routes were apparently very adept at picking up accents of pilots who might not be US/British/French, especially on charters and biz-jets. THey could even distinguish Canadian from American.