Today's episode of "This American Life" on NPR discussed the experienced of language-less people (generally speaking, people born deaf who are not part of a community with a sign language), including the experience of Nicaragua where the formation of a special education school that united fifty language-less deaf people for the first time led to the formation of a new sign language from scratch which has developed over forty years. It is arguably the only instance known in which a new language has been observed coming into being from scratch on a grass roots, natural basis, as opposed to as a "constructed language" (a.k.a. a "conlang").
The big take away from the episode was that it convincingly demonstrated that it is very hard to think about ideas, especially intangible ideas like what someone else is thinking, without having words to describe them. At a quite fundamental level, it is not possible to engage in many kinds of thought without language to describe things.
Moreover, learning words to describe new concepts, even at middle age, can open up your ability to think about things that you never in your life until you learned those words could think about, and learning those words can open up that world to you in a matter of a couple of years or less.
In the case of the deaf Nicaraguans who created there own sign language which became much more polished, stylized, hand oriented and was extended to describe intangible things over the course of about 30 years, starting out with just two thought words ("know" and "don't know") in the first generation, and expanding that to about ten more words for thoughts over the next thirty years, made an immense difference in the ability of speakers of this sign language to solve real world problems calling for empathy about what someone else was thinking. And, as younger speakers in a cohort that had added these words to the language created by the original cohort of fifty kids began to interact with their older peers, in a matter of a couple of years of this informal interaction, the older peers learned these words and were able to think about these things successfully and apply them to real world situations in ways that they had not been able to do so before.
There is also an implication that these insights might have application well beyond the world of people who lack language. People who for whatever reason were not exposed to words for key concepts might find that their intellectual functioning by learning these words. And, similarly, if we devise or popularize new words for new key concepts that are not present in an ordinary educated person's vocabulary, we might improve the ability of already functional people to function in new domains that where people previously were bad at thinking about things.
In other words, one powerful form of cognitive-behavioral therapy could simply involve teaching new words and concepts to people, which would open their horizons and make them able to think in these new ways whether they wanted to be able to do so or not.