Thank you very much for sharing your thoughts and info. Being multi-lingual myself, I certainly understand the concept of language immersion (and, actually, most recently have tried it partially with Mandarin, in the form of watching Chinese movies, mostly with subtitles). However, I doubt that it is possible to learn correct grammar from language immersion (it's probably not that important for languages like Mandarin, which, as I understand, are very lightweight in terms of grammar; but, for the rest ...).