Language
System of signs allowing the expression and communication of thought. It determines thought, can be non-verbal, does not create truth but signifies it and has multiple meanings (polysemic).
Descartes
Animal language is only the expression of its bodily needs, it only speaks to satisfy its body (hunger, thirst...). When an animal expresses itself, it is rather a signal that triggers an action and not a dialogue. Human language is the expression of our mind while animal language is the expression of the body.
Dominique Lestel
"Animals can speak but have nothing to say," they express bodily needs but do not tell stories.
Hegel
If language did not exist, would we be able to develop thought? Hegel thinks not, "thought without language would be obscure thought," i.e. thought that would be trapped in our subjectivity (feelings, emotions). Language allows us to make our thoughts objective, we can expose them to others, they become real, while our subjective feelings are blurry until we put them into words (lowest degree of thought) = ineffable, but for him it is the most obscure degree.
Freud
Language is not only a means of communication but also a means of expressing our unconscious. Most of the time, we repress our unutterable desires and traumas. It is not by repressing our demons that we are happy, but by confronting them through language.