You already know several ways to represent the same words in the language. You can see it written down or you can hear it spoken out loud. When you know one it does not take much effort to learn the other. This is what kids learn in kindergarden or early elementary school and why these classrooms all have the alphabet with pictures of things starting with that letter. It is so the kids learn to associate a written letter with a sound.
Deaf people all learn to read and a lot of them also learn to spell using sign language or even reading lips. So they already know the language, they just don’t know the sounds associated with the letters. When they get a hearing aid they can start learn this. It is just the reverse of what children learn in school. Except it is usually easier to teach adults as they have lots of motivation to learn this for themselves.
When you see videos of people as their hearing aid gets turned on they are not communicating through sound. It is too early for this. But they are already very good at communicating without sound through various means. There is often a sign interpreter off camera, this might be a close relative or it might be a hired sign interpreter. You often see this as the patient tends to look at something off camera even as doctors right next to them are speaking to them.
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