For example, in the movie Ip Man, the "northerner" martial arts fighter who comes to Foshan to challenge the local martial arts fighters always talks in Mandarin, while everybody he talks to (the local citizens, fighters, Ip Man himself, factory workers, etc.) always speak to him in Cantonese. This is repeated throughout the movie. The conversations are carried on fine with both sides seeming to understand the other perfectly, and both sides assuming that the other side understands them, even though Mandarin and Cantonese are not mutually intelligible. Neither side tries to change to the other side's language, and neither side is annoyed that the other side continues to speak the other language. This seems really odd to me.
Is this realistic?