A related notion is that when you really know a language, you think in it. In fact, the brain doesn't think in any language. What people refer to as "thinking in a language" comes from being able to speak more immediately in a language without rehearsing it or translating it from a language one might know better; the spoken thought feels as if it's closer to its source in the brain.
Michael Erard, Babel No More: The Search for the World's Most Extraordinary Language Learners
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