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Marrying someone who can't have children, marrying someone from another culture, and marrying someone your parents disapprove of are all pretty big deals. Does he want kids? Have you asked? Does he want a wife who will celebrate the same holidays he celebrated growing up? Do you know? It's possible for two people who are dating, and even living together, to construct a private world where the hard questions are never asked. Eventually, the private world won't be enough, and everything you fail to ask now will bite you in the ass.
Assume you give him an ultimatum and he says yes. Ten years from now he looks at you across the dinner table and says, "I don't have parents, I don't have children, I don't even have a wife who can speak the language I grew up speaking; all I have is you, and you aren't worth it."
Think about that before you pressure this guy into doing something he has demonstrated an unwillingness to do.