The OP made me think about what my own thinking process is like. There are clearly thoughts that are, for lack of a better word, nonverbal. If a plate is falling off a table, I reach over and grab it without thinking the words ‘I should grab that’. In fact I would claim that most of my thinking is nonverbal, in that I formulate plans and act on them without a voice in my head saying, mentally ‘out loud’, “Now I should turn left at this intersection, then slow down at the next curve”. There’s rarely a ‘voice in my head’ unless I’m planning what to write or say, or reading, or doing a math problem. Otherwise, I don’t typically narrate my actions or plans to myself. Maybe, while leaving the house, I’ll pat my pockets feeling for phone, keys, and wallet, thinking ‘(affirmative grunt), (affirmative grunt), nope’ but not thinking “Let me check to see if I have my phone and keys and wallet. Yes, phone is there, Yes, keys are there, but whoops, no wallet”
I suspect that the thinking of persons deaf from birth is like this; the ability to reason, plan, and act without an internal monologue that consists of a voice in your head. I also suspect that the opposite is true for some people; those that seem to need to speak aloud in order to think - or perhaps can’t think without stream-of-consciousness narration.
I think it’s quite possible to formulate a plan to go to the store, decide to do it, and then explicitly ‘say’ ‘out loud’ ‘in your head’ “I’m going to go to the store”, as though you were saying it out loud with your lungs and mouth.