> 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.

This is not even true, plenty of people think in think in their second language.

No, because we are talking about the foreign person trying to learn the new (second) language by total immersion. They obviously aren't going to start thinking in the second language until after they've learned it.

You can start thinking in the second language before you have fully mastered it.

Sure but what happens if you try to think of a word you haven’t learned yet?

Circumlocution. In this case, circumcogitation.

Desh walowda we fo du owbit owta we. (there's more than one way to transfer orbits)

> 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.

Not exactly. One of the first signs that you have made substantial progress in a foreign language is that you no longer have to translate your internal monologue when speaking.

If you are by yourself, then reverting to the native language can happen. That's assuming you can even 'hear' your internal monologue, that's not a given. Would this impair language learning?

What about children exposed to multiple languages from an early age? Surely the external voices wouldn't always match what's in their head - they still learn very quickly.

Clearly brain plasticity in a youthful brain helps immensely. My point was just that it’s not that straightforward to compare kids with adults in regard to language acquisition. An adult always has an ‘inner voice’ in their original language at first, so there can never be complete immersion as there can with a child who comes to the table with, originally, a blank slate. Or, at the very least, with an ‘original language’ inner voice that isn’t as robust as an adults. That is, I would suspect that an adult’s ‘inner voice’ has a far richer vocabulary and formal grammatical structure than an 8 year old’s ‘inner voice.’

Stated differently, an 8-year old with English as a native language has and ‘inner-voice’ of an 8-year old: limited English vocabulary and limited English grammar. If you immerse the kid in Chinese, that immaturely developed inner-voice isn’t much competition to what’s coming in through the ears. A 40-year old, of course, has an ‘inner’ English voice that is completely formed and has been in habitual use for decades... much more competition to what’s coming in through the ears. Indeed, as other posters have noted, when learning a new language, one must make a concerted effort NOT to translate the new word in one’s head, but rather to let the new foreign word stand on its own two feet. This is easier for an 8-year old, I would think, as there will be multitudes of new foreign words they are hearing that don’t correspond to anything they’ve yet to learn in their native tongue; that is, there are a lot more words for which they won’t be tempted to ‘translate’ into English as they haven’t even learned the English word yet (or, at least, haven’t known the English word that long.)

I think this may be why it’s easier to pick up food words. I know what ‘burrito’ means as an English speaker, because I can’t translate it into English... the word stands on its own two feet. But, the word for ‘stew’? That doesn’t stick as well as I instinctively translate the Spanish word guisado into ‘stew’ in my mind.

Adults have a better capacity to learn foreign languages.

It's just hard cause you have to re learn the system you know unconsciously.

This is simply false. E.g., my kid is around speakers of 4 rather different languages. At age 3, he has grasped all 4 languages to a good degree and even translates pretty well between them. I don't think he's particularly unusual and 3-4 language speaking kids are reasonably common around here.