I'd think the main differentiator between humans and other animals, is that refined language gives us the ability to 'know' infinitely more properties, properties that give us a greater ability to manipulate the world.
It takes a certain level of "intelligence" to be able to work with a language. You can't have a complicated language, like human language, without having that level of "intelligence" first.
One of the key elements of language is the ability to conceptualize.
Words don't relate directly to things in the world, they relate to "mental concepts".
So we can use the word "tree" to refer to all kinds of things that look very differently from one another because they are all included in our "mental concept" of "tree".
A concept is the result of what we expect from intention. A chair is something we can see as intended to be a chair.
Language is the mirror of intention.