It is said that all intelligent creatures have an advanced language. It is what sets intelligent creatures apart from the Solarians. It is the ability to handle ideas. Even the Treecat language resemble human language in some of the similar "notions" born of the language itself. Such as "speaking" to each other.
I think Harold was hearing grammar, verbs, etc., when I speak of a 'Cat language. Although, I would suspect that grammar has its place in Treecat language as well. Language has to have structure. Grammar is structure.
At the end of the day, language is all about the communication, not the construct. Sentient beings CANNOT think without a language. Unless you know everything already, therefore don't need language. Like God?
Human language is based on the spoken word. Treecat language is based on the spoken thought. Which implies a lot more efficiency, if you consider that a single human thought can comprise a long post. And instead of body language and mannerisms to augment the communication, there is emotion. A sentient being having thought as the basic building block of their language is incredible. I can also conceive of why it could be a hindrance to learning technology.
There are profound questions remaining. Consider that computer languages are not created equal. Some are simply not up to specific tasks. Is Treecat language too specific or too limited in some manner to accomplish learning technology? Their language evolved in the wild. It had to serve a purpose of survival amongst deadly creatures.* Their language may have evolved for survival first, instead of the luxury of great scholarly thought. I don't imagine there are any Platos amongst the Treecat species. Not because of a limited intelligence, but because of necessity and a priority of life - a language evolved for other purposes. Memory Singers are their repositories, their libraries.
I'm willing to bet that coexisting with humanity is going to alter the Treecat language profoundly over time. Two-legs are the Treecats' volcano I spoke of earlier.
At any rate, a being cannot think without a language. Even in the unlikely event that he can communicate without one. He still has to think. And thinking IS NOT generic. Or all Treecats will have the exact same description of two-legs. Ridiculous for anything but a bunch of automatons. The Borg!
Without language, there can be no thought. Without language, there is no intelligence. Period.
* In some scientific circles, it has been proposed that man was once telepathic himself. It was the result of living amongst the dinosaurs. The first at the top of the food chain. Self explanatory.

Oh, before anyone mentions it. Man supposedly did not live amongst the dinosaurs.
Because. they. were. all. eaten!