It seems to be unknown how many people speak ASL (American Sign Language). According to a citation from almost 50 years ago, Wikipedia says between 250,000 and 500,000 people, primarily in the US and Canada. Sign languages in other countries, including Great Britain and Australia, are unrelated to ASL.
About 10 days ago, the Goshen News ran a feature on an ASL interpreter named Colleen Geier, who, despite growing up around a great-uncle, did not learn ASL because he was not allowed to sign.
Fortunately, attitudes have changed, and ASL is a thriving language used by deaf and hard-of-hearing people, as well as hearing people who can sign.
Check out the article and read about some of Geier’s adventures, including one with a Secret Service agent!
(Words such as “speak” and “talk” are applied to sign languages as well as spoken languages.)