If you are fluent in a second language, you understand that the only way to become truly fluent is not just to learn the tangible aspects - the vocabulary, grammar, references, expressions, etc - you have to learn to think like the language/culture.

It’s a combination of cultural assumptions, facial expressions and affectations, thinking patterns, and a whole cultural upbringing that can lead you to very different mental processes and natural conclusions starting from the same words and phrases.

Language absolutely encodes a certain form of intelligence. A lot of those things are reflected not just in the totality of the culture but the language itself. Being fluent leads you to different thinking patterns and different conclusions when processing in that language.