That's funny because I have lived in California my whole life. As a hairdresser when someone had an accent I would ask them about then ask questions about their country. I think maybe cause my dad is from Portugal at came to the USA at the age of 17 that I'm not to worried. If you are polite and generally interested in what different cultures no one is offended. I did hair for 14 years, my ear for asian accents is very good now.
To me a person from Vietnam sounds nothing like someone from Japan. Cultural these areas are worlds apart also. It surprises and delights people when I correctly guess there country of origin. Political correctness is drilled in our heads down here.
I never want to offend someone so I'm careful about the things I say.