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.