The department had a trio of Indians in the early 80s at my alma mater. Learning to understand their accents was definitely a trick.
I do have to say I had a Frenchman who was professor in a history class...Not only could he speak great English, but he would come to class wearing the apparel worn during the time we were studying...
He was fantastic...Dr, Burgeron....
I had a calculus teacher at the University of Arizona that was the same way. He mumbled at the blackboard in a dielect that none of us could understand. I ended up dropping the class.