> "First" and "last" is a wrong representation anyway, because it assumes people always write their names in that order.

I do not see this as a problem. If i know English so i can fill english-labeled form on english webpage, i would also have a bit of cultural knowledge to translate first name to given name and last name to surname.

> But this has it own issues, like assuming people have either a given name or a surname in the first place.

This is only a problem if the form validates that both fields must be non-NULL. Problem is not with the split itself but with the validation code.