UW Madison not only offers Turkish (even as a major) but also hosts the Turkish Language Flagship Initiative. Turkish – UW-Madison Languages – UW–Madison
if your son loves both math and languages, has he considered studying linguistics? Computational linguistics might tie a lot of his interests together. There’s an annual competition for high school students that might interest him and introduce him to the field: https://nacloweb.org/ There’s a large collection of practice problems on the website.