In this case I'll start out with two questions and maybe others can add more as this thread goes on.

This is an honest question I've always wondered about. Assuming someone is deaf their whole life and has never heard sound nor has any means of communication, including sign language, what exactly would their inner monologue "sound" like and how would they organize their thoughts at all?

One more that is essentially in the same vein as the first. As far as I know everyone's own inner voice is in their "own" voice. What if someone is unable to make any sound, i.e. totally mute, what would their inner voice sound like?

As to the first question I couldn't imagine.  Possibly their thoughts would be more pure and concise, not encumbered by the restraints of language.  This reminds me of an old Outer Limits episode where a little girl, Elsa I believe, was never taught to speak by her parents.  Instead they communicated with her telepathically only.  Consequently she learned at a greatly accelerated rate.
For the second question again I'm  just guessing.  Possibly they would adopt the voice of someone close to them as their inner voice.
Of course there are real answers to these questions but finding them might require a great deal of searching.