We think in images as well, surely?
Images and feelings too, yes. There was a research I heard about where it was proven that people could traumatic experiences if they got rid of the feelings connected with the experience.

It makes sense as the survival of a person/animal depends on rembering what causes pain (bad) and what is nice (good). If there is no feeling associated with a past experience then it doesn't affect the chance of survial, as a result it can be forgotten.

I tend to see my past as more of a film, maybe the narrative might not be present were I to lack a language, but the pictures, sounds, smells... would still be there.
Our dog sometimes growled and moved his legs a bit when sleeping, just like I sometimes do when having a nightmare. That convinces me that animals can dream, why else would the dog do that? Dreams require having images in your mind. So animals can have images in their mind. Wouldn't that mean that animals could somehow "think" with images and feelings?

There are "funny home videos" of dogs moving chair around to use it as a step to get on a table. To do that the dog would have needed to form those actions in their head. It is not instinctive behaviour. The same with apes using sticks to get honey out of holes. It requires thought, if only to see in their mind how the chair being closer to the table enable them to get on top of it.

And to complicate things even more. What does a person think who is both blind and deaf from birth? He cannot form images and cannot form words. The only thing left is feelings. Yet those persons are still able of doing complex handlings.

Having a spoken language would thus merely improve/upgrade the way of thinking, but it is not the only prerequisite for forming thoughts. Is that a plausible theory?

It seems that I am already coming to a conclusion with all this reasoning. Far too soon for my liking. So please let hear your own thoughts!