According to Ethnologue, there are 114 sign languages around the world. The most widely used is American Sign Language (ASL), with an estimated 500,000 to 2 million users, according to this site. Probably the next most widely used is British Sign Language (BSL), with up 250,000 users, between 30,000 and 70,000 of whom use BSL as their first language, according to the BBC.
Does anybody know whether there are any sign language polyglots – those familiar with many sign languages? Or whether there are many blind people who can read many languages in braille? I wonder what kind of challenges users of one sign language face when learning different sign language, and how difficult would it be for blind people to learn another language through braille.