Question about The Languages.

My biggest complain with this film (which are quite many) is the scene where Klaatu has a conversation with his fellow being in Chinese and then then change the language to English without any explanation. What is the point of all this? The conversation was already in Chinese so it's not valid point to say that people don't want to read subtitles (which is a stupid point anyway).
I have never seen any normal people who change their languages like that in the middle of conversation. Not even with a people who are bilingual. The only way that this would happen naturally is when there is another person introduced to the conversation and everyone changes their language accordingly. To me it seems that that is what was supposed to happen in the film, but then for some reason it didn't (but the language was changed anyway).