Hello Unilang,
I have been studying Japanese for the past few years and I recently got the chance to work with a group of Japanese exchange students which for me was very much like an immersion. After that I really believe I got a truly great understanding of Japanese conversation and I was able to speak quite fluently. I am still studying though. This summer I'm heading to Beijing for two weeks and I really want to take some time to get a good understanding of the language before I go, mostly because I have some experience with it and the language really does intrigue me. Would it be smart to throw in another language into my head so soon or do I have a chance at retaining the information of both languages and be able to file them properly. Also, if there are any good materials for learning Mandarin out there that you know know of I would really like something to study with, I like to focus on grammar and conversation primarily.
Thank you.