They say that to truly understand a language, you must not translate each phrase in your head, instead you must think in the language you are trying to learn. We all have an inner monologue, and although most of the time we do not take note of its language or accent, it is there.
When children learn a second language, they are unaware of what they are doing, language is a concept created by adults, but to children, it is just another way of communicating, this is why children who are raised bilingual do not translate phrases in their head, they think in the language.
So what about dreaming?
When dreaming, those who speak one language generally tend to dream in that language, but for polyglots, the language that they dream in varies. Stranger still, there have been many instances of polyglots speaking a language fluently in their dreams that they are not able to speak fluently in life. Is this because our brain remembers everything that we learn but when we are awake we are not able to access it?