The movie 'A Thousand Years of Good Prayers', which features Mr Shi and his daughter, Yilan as its main characters, is not much difference with 'Japanese Story'. The characters in both movies dont talk much but, instead the movies focus more on characters' body language.
So come to answering the first question on why is it so hard to talk to each other, the answer will all be about difference. Firstly, it will be the difference in perception and belief. When two people believe on two different ideas, it is most probably that they will end up arguing with each other. Basically in the movie, Mr Shi as an old man with traditional thinking believes that, a happy person will not keep the happiness alone. He or she will talk in order to share their happiness with others. Yilan on the other hand, disagree with that. She thinks a person can keep silent even when he's happy. In the movie, Mr Shi and Yilan argue about lots of things, mainly because he and his daughter spent most of their life in two different places, China and America respectively.
Next, difference in language. People use language to unite them but if the language itself is different, of course its' hard to remain close with each other. Mr Shi and Madam who is from Iran, obviously have different native tongue. In the movie, they speak English but still they hardly communicate well, take a simply long time to think of the appropriate words to use. One of Madam's dialogue is, "America good country, sons make rich money".
Not only that but its' also about a difference in gender. As typical Asian, Mr Shi looks uncomfortable talking to the blonde girl, who at the time wearing only bikini. He tries to give uneasy look as the girl gets up from her chair and approaches him. In the end, he excuses himself and walks away from the place. Anyone who watches that scene can confirmly tells that it is quite a tense moment, as the conversation does not happen smoothly.
Besides that, the movie also deals with the issue of emotional war, especially Mr Shi, who appears to keep secrets from his family. He tells no one that he's no longer a rocket scientist after the age of 32. Generally, there is only a single solution to this problem that is by talking and expressing feeling to someone. One says 'sharing is caring' and that's really sum up everything.