Those two questions have always puzzled me
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You don't think in language, you think in ideas and concepts. If you actually had to say everything you were about to do 'aloud' inside your head before you did it, you'd function extremely slowly.
There have been numerous cases throughout history of 'feral children' who never learned a language. There is a critical period for developing that part of the brain, usually before the onset of puberty, after which it is borderline impossible.
The case of 'Ildefonso' is what I am specifically thinking of, because when he acquired language after 27 years, they asked what it had been like living purely from instinct before.
“I think differently. I can’t remember how I thought.”
I think that language encourages a kind of cognitive development that shapes how you think and reason. But you don't consciously think in words and sentences (unless you are planning out what you're going to say or write)
A person who was born blind has no concept of sight and images, and won't have any imagery in their dreams. Someone who became blind later in life will likely have some dreams with images.5