In English, you just simply say “hi”, or “hello” to a person.
In Vietnamese, you can say “hello”, or “chao” [jao] , or “xin chao”.
Hello is universally accepted in Vietnam. But not “Bonjour”. I can’t believe how nearly 100 years of French domination in Vietnam and the Vietnamese no longer, neither ever accept greet “Bonjour” or “Bonsoir”. But Hello is so naturally accepted.
Yes, “Hello” is considered very polite at any ages in Vietnam now aday.
But to correctly greeting Vietnamese people, it is most important with how you say “hi” to a very specific age group and sex.
There are many ways to say “hi” to Vietnamese people.
Same age group. Two persons can say “Hello”.
But Older aged person never say “hello” first to a younger person.
Same age group. If you are a guest, walking into a cuisine.
You say “Chao Co” or “Chao Chi”, if the waiter is a female.
You say “Chao Anh”, if the waiter is a male. There is rarely “Chao Chu” (Hi uncle, or young man).
A younger person says hi to an older man: “Chao Bac” (like Hello Grand Uncle)… if you know the older man is actually agely older than your father. Else “Chao Chu” if the man is likely younger than your father.
Vietnam’s way of greeting is considered a way to show how much bonding you are to a person. It can be very complicated, yet, that is also the secrect to making Vietnamese a natural spy when foreign invaders intercept Vietnamese society. That story can be regarded to Pham Xuan An of Vietnam.