Michael Erard said this quote

If you want big improvements, she said, chew gum. Gum? Sure enough, chewing gum has been shown to improve a person's immediate recall of learned words by some 24 percent. Long-term recall improves by a larger 36 percent. To get the benefit, you actually have to chew gum as you are studying; for some reason you can't merely move your jaw up and down. I also discovered that drinking sage tea increases one's recall of words modestly, as does the odor of rosemary. Something as mundane as coffee provides a benefit, too. Drinking two cups of coffee increases neuronal activity in the frontal lobe, where working memory is controlled, and in the anterior cingulum, where attention is controlled.

~ Michael Erard

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

What you see and hear is a situation in which languages are less like apples — neat and discrete — and more like oatmeal. It's always been oatmeal in India, and all the varieties of oatmeal continue to merge, despite political pressures to name them as if they were marbles.

~ Michael Erard

Possible explanations for talented language learning fall into two general areas. One view says: What matters is a person's sense of mission and dedication to language learning. You don't need to describe high performers as biologically exceptional, because what they do is a product of practice. Anyone can become a foreign-language expert - even an adult. (...) The other view says: Something neurological is going on. We may not know exactly what the mechanisms are, but we can't explain exceptional outcomes fully through training or motivation.

~ Michael Erard