There are several ways to say "sign language" in Spanish: -Lengua de signos -Lengua de señas -Lenguaje de signos -Lenguaje de señas All of them are equally correct and are used as often. So pick one of these combinations and add "americana" (if you pick 'lengua') or "americano" (if you pick 'lenguaje'). So you'd say: Estoy aprendiendo la lengua de signos americana. Estoy aprendiendo el lenguaje de señas americano. Etc. Cheers!