> An adult, on the other hand, can never be immersed into a new language like a child. Even if an adult is in a foreign country 24/7 without any speaking his na

> An adult, on the other hand, can never be immersed into a new language like a child. Even if an adult is in a foreign country 24/7 without any speaking his native language, the adult will still hear his native language in his own head; that is, the adult will think and talk to himself in his native language and will always be a competitor for the external voices he hears. I am a native English speaker who learned Italian in my 20s. When I stay for a week or two with my Italian in-laws who don’t speak English, I find myself thinking in Italian after a few days. It’s noticeable because my mind will wander into a topic about programming or something and my internal monologue will hit a technical word that I don’t know. I also dream in Italian and report this to my Italian wife. It’s not hard to slip into. I think your claim is based on speculation, because my experience says otherwise.