I'm sure they have a huge Chinese American team research and contribute to the script.
Born in Hong Kong, growing up in Canada, and moved back to HK 9 years ago. I was surprised how much they made it right on the traditional Chinese, and Chinese American culture. From the living style, the believes, the family dynamics, also the way we talk to each other, mixing both Chinese and English sentences and phrases, they just feel so right. When Shang-chi and his sister speak Chinese(Mandarin) to each other they sound so natural like they were a Chinese family.
And for some people argue about the Asian or Chinese representation this film brings. I understand what they mean. I mean, I have lived in Canada since 1997, whenever there's a movie with an asian lead character me and my brothers would be super excited to go to the theatre to watch them. Like Crouching Tiger Hidden Dragon, Jacky Chan's Shanghai Noon, Jet Li's Kiss of the Dragon, etc. But to be honest, they are nothing like Shang-Chi. In those Jacky Chan and Jet Li's films, they always play this stereotype, fresh off the boat Chinese person doing action and kicking butt because that's the representation of Chinese, under the shadow of Bruce Lee. But Shang-Chi is an Asian-American, who's grown up in America, and he is a part of the community of the American culture. He doesn't have the representation of FOB Chinese, because he's always been around and grew up with everyone in the city. For this group of Asian people (like myself), their identity falls in between the East and the West. Just like Ronny Chieng says in the film "I speak ABC." <- This actually represents the identity of American-born Chinese.
I think Shang-Chi did something really special for this group of people, it feels like Shang-Chi really help people to understand the culture and life of their Asian friends growing up around them.