how do adults learn languages?

I would like to pose a question on what seems to be the (rather popular) idea that adults can learn language in more or less the same way as a child does, i.e. in a purely communicative way which abhors any mention of the students L1.
The question is: do you believe a student can understand a foreign language by any means other than in terms of their native language and, furthermore, is it possible for a someone to learn an L2 (very different from their own) solely through speaking - without studying the grammar, but nevertheless end up speaking with a high degree of grammatical accuracy? (a long question, I realise)

I think when an adult tray to learn foreign language that person is thinking in his/her language but when a child learn foreign language his/her brain does not be corrupt yet I mean if you have a fresh mind it will be easy to learn anything that you want to lean or to do.

Learning a language is combination of things – regardless of how old you are. Most adults struggle because they have difficulty changing their habits. However, changing your habits is the most important requirement when it comes to learning a second language.[YSaerTTEW443543]

TOEFL listening discussions: What is the design of the sweatshirt?[YSaerTTEW443543]