I knew someone who was deafblind who’s L1 was Polish, which he learned to speak as a hearing child. He taught himself how to speak English after he lost his hearing, using the pronunciation key in the dictionary. Consequently, his Polish was much easier to understand (according to a Polish-speaking colleague at the time) than his English, which was spoken with a thick accent. But he was still understandable in English. So yes, I’d say it’s possible for someone completely deaf and blind to learn a second language, because I’ve seen it done. Probably doesn’t happen that often, though, because it must take a lot of perseverance.

$1.

> At first, Helen had studied French mostly on her own. She had a French grammar book which she was able to study on her own because it had raised print. In addition to this, Helen "often amused [herself] by composing in [her] head short exercises" in the French language (The Story of My Life, Chapter XVI). She even tried to perfect French pronunciation, which was a difficult task because she could not hear any examples of it. Instead, she followed the written descriptions of the pronunciations. Helen also enjoyed reading French literature for pleasure. This strengthened her knowledge of French vocabulary and grammar.

>The next year, Helen started attending the Wright-Humason School for the Deaf. This school was located in New York City, so Helen relocated there with Miss Sullivan. At the school, Helen took formal French lessons with a teacher for the first time. She found French to be challenging at the school because her teacher did not know the manual alphabet. Helen had to press her fingers over her teacher's lips as she gave the lessons. It was difficult for Helen to learn this way.

A $1 is what people traditionally use to write Braille text; I don't know if that's what Helen Keller herself did.