Adam Clarke on Genesis 42:23

For he spake unto them by an interpreter - Either there was a very great difference between the two languages as then spoken, or Joseph, to prevent all suspicion, might affect to be ignorant of both. We have many evidences in this book that the Egyptians, Hebrews, Canaanites, and Syrians, could understand each other in a general way, though there are also proofs that there was a considerable difference between their dialects.