Re: Does the name Olivia sound okay with the Vietnamese last name Tran?
Yes, it sounds fine. The sounds of the names don't clash or blur together, it doesn't combine to make a funny word or phrase, and Olivia isn't so noticeably "ethnic" (like say, Saoirse or Rivka) that it makes the combo feel odd.
Although, I will say, I know a boy of Vietnamese descent, a friend of my daughter, whose name is Enrico. It sounds odd with his last name, but only in a momentary "Well, that's unusual" kind of way.
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Steve Martin