@dgar@aus.social as a general rule, the only overlap with the spoken languages is words you fingerspell, although other signs often incorporate first letters. The main thing will be whether the two people sign the same sign language, or closely related ones. There's a whole historical split between Protestant and Catholic schools for the Deaf that explains which sign languages across Europe are derived from the French vs the British type. American sign language is the French type, and the full story behind it is fascinating!