I flew for a European freight airline for almost 20 years. We started in UK, moved to Germany and then to Belgium. The crew room at night was full of old American boys who flew the Super Connie for Eastern to Ukrainians who were constantly arguing the benefits of the Tu-204 with RB211s versus the Russian version with P90s.
We ended up in the south of Belgium where the local language was French, working for a company based in Holland. The official line was that the "official language was French but the Working Language was English." (That made my American colleagues feel better!)
This system worked very well and we were all able to communicate.
Belgium is a very interesting contry when it comes to speaking foreign languages. There are two main languages; Flemish (Dutch) and French. But there are about 10,000 Belgian citizens who live around Aachen who are German speakers.
So, a pilot in the Belgian Air Force for example, has to speaK AT LEAST THREE LANGUAGES, for everything to do with aviation is conducted in English!
This ensures that the Dutch speakers do not have any advantage over the French speakers etc.
In 20 years, I had enormous fun flying with all of them and I have to say that it was the best flying job that I ever had.