I am currently performing a cross-linguistic investigation of determiner phrases, and I was wondering if there are languages out there where an overt determiner can occur with a pronoun or proper noun, such that an example like "the Mary" or something along those lines would be grammatical. Thanks!
Lots of languages precede proper names with a definite article. The phenomenon is called the 'preproprial definite article'. You can find an article with a quick survey of languages and some theoretical conclusions here:
The main theoretical conclusion that people draw is that proper names are definite descriptions cross-linguistically, even in languages like English where this is not overt. This recalls a position set out by Bertrand Russell (1905, Mind). A more recent development of it that has proven to be quite influential among philosophers and theoretical linguists can be found here:
As for other determiners, English and some other languages allow you to say things like this:
i) I met an Alfred Russell yesterday. ii) Every Alfred I ever met was a baboon.
There is some debate over what is going on here, but people like Delia Fara, whose article I just gave a link to, think that names are basically predicates and so the names that appear in constructions like this are unmodified names appearing with determiners, just as nominal predicates should. Further references can be found in her article.
As for determiners preceding pronouns, I know of no such case--well, with the exception of 'Is it a he or a she?'. I do not know what is going on there!