It would be a mix for me. (I mean deaf and mute people still have a thought process even if they have never heard the language as a voice in their head--I assume) Sometimes it can be an internal monologue, but other times, especially doing engineering tasks, there are no words it is just visualization of steps or process or concepts. i also have noticed that if I'm thinking in language I can type it very fast and it flows, if I try to talk to people the act of verbalizing interupts pulling the words forward in thoughts. And I have to pause to think of words or process for a sentence. The only way this doesn't happen is for very rehearsed topics.