Language is not essential for the cognitive processes that underlie thought

Serializing much higher dimensional freeform thoughts into language is a very lossy process, and this kinda ensures that mostly only the core bits get translated. Think of times when someone gets an idea you're trying to convey, but you realize they're missing some critical context you forgot to share. It takes some activation energy to add that bit of context, so if it seems like they mostly get what you're saying, you skip it. Over time, transferring ideas from one person to the next, they tend towards a very compressed form because language is expensive.

This process also works on your own thoughts. Thinking out loud performs a similar role, it compresses the hell out of the thought or else it remains inexpressible. Now imagine repeated stages of compressing through language, allowing ideas to form from that compressed form, and then compressing those ideas in turn. It's a bit of a recursive process and language is in the middle of it.

> this kinda ensures that mostly only the core bits get translated

The kinda is doing a lot here. Many times the very act of trying to communicate a thought colors/corrupts the main point and gives only one perspective or a snapshot of the overall thought. There's a reason why they say a picture is worth a thousand words. Except the mind can conjure much more than a static picture. The mind can also hold the idea and the exceptions to the idea in one coherent model. For me this can be especially apparent when taking psychedelics and finding that trying to communicate some thoughts with words requires constant babbling to keep refining the last few sentences, ad libidum. There are exceptions of course, like for simple ideas.