Oh yeah - I was in my favorite deli, owned by a Korean fella and his Chinese wife, when a curious customer asked the owner if he was Japanese. He was visibly offended!
I think it's kinda silly that, by the 23rd and 24th centuries and after another World War and the Eugenics Wars that everyone from Earth is still considered pretty homogenous.
In my idea for a fan fic I had a female Captain of mixed Asian decent. One of her parents would have been mixed Chinese/Japanese ancestry and her other parent would have been mixed Korean/Vietnamese ancestry (or some other multiple combination for both parents). She would have spent summer and winter vacations at her grandparents and, as a result, would have a vast and varied background and interest in different Asian cultures, customs, foods and dialects.