In the movie "Schindler's List" people are talking mostly in English and German. Since the movie is about Jews and Germans in Poland, they should talk in Yiddish/Polish and German.
I can understand that they did not want to use historically/geographically correct languages (this is common in many films) and they switched to English and German.
However, every now and then you can hear a Polish word, which sounds off - why have they decided to use this language?