My best friend in architecture school would ask for a pin and I never knew if he meant a writing pen or a stick pin. My best professor in college, I think I only understood half the words of his first lecture, but eventually I got used to his strong Austrian accent. I find Asian accents harder to follow, I think because they don’t get the tonal flow of sentences and they’ve usually learned British English. Your son is likely to find hard to understand accents at every level. He can certainly talk to the disability office and see if they can help. I think also that talking with the people you find hard to understand one on one may help. It’s really not just a TA thing.