As you are aware, this site is called “All Japanese All The Time”, reflecting the fact that I shoehorned Japanese into every little crack and corner of my life in an effort to get fluent at it.
I don’t know the full extent of the effect that this immersion project had, but I read a forum post somewhere where someone had suggested that the immersion environment was merely motivational and didn’t matter as much as doing sentences. With this I must respectfully disagree. Let me discuss just a few of the reasons why the immersion environment is so important.
Before I get to that, let me note that I don’t think that there’s such a thing as “just” motivation. What I mean is, it’s not simply this nice thing to have, like one of those compressed-air spraycans for cleaning your keyboard (those are nice things to have :D). Like it or not, humans are made and broken by their emotional state and belief in and about themselves — or lack thereof. It’s not some magical cosmic thing (even if it were, it doesn’t need a magical cosmic explanation). Things like the Pygmalion and Placebo Effects, respectively, have been empirically observed and testify to the importance of mental condition. Your thought patterns matter; your state of mind, matters. People who are motivated and thus expect to do well, tend to do well, one way or another.
Back to a more concrete discussion of immersion, let me first note that the immersion environment was itself a source of sentences. Furthermore, I got used to hearing Japanese spoken at native speed with native intonation, native pausing, native mumbling, native bridges, native nuance and all that good stuff. This is priceless, and even if it’s not explicitly contained in the sentence collections I made, it had an effect. I am a HUGE fan of people focussing on text, non-native illiteracy in Japanese is inexcusable, but there is more to this language than text.
Finally (getting to the main point of this post), one thing I am noticing in the Chinese Project is that the environment shapes the way you learn the language. Simply put, it’s a usage thing. It’s the Pareto principle at work — in any language, some words and phrases get more usage than others. So, like, maybe 20% of the words and phrases get used like 80% of the time or whatever (do you like my fuzzy statistics?). This means that the more Chinese you read and hear, the more the same things keep popping up over and over and over again: even if you don’t know what they mean, you eventually HAVE to find out because you KEEP hearing them; they force themselves to your attention. Things like “根本” as in “你根本不知道・・・”, things like “別作夢了！”. I wouldn’t have realized the importance of these words/phrases if I were just looking up random sentences. I am learning them and learning to use them because I hear/read native users of Chinese (in my Chinese immersion environment) use them all the time. As a result, my Chinese will become more native-like — I am not going to learn every word in the Chinese language, just like I don’t know every word in the English language, but I am going to learn the words that matter and I am going to use them the way Chinese people use them — I won’t be falling into that non-native trap of using words that have the right meaning but that are inappropriate because they are either too obscure and formal, or too colloquial and informal, or carry a bad connotation in the situation at hand. This won’t be a conscious or effortful thing, it will be the natural and effortless result of being surrounded by Chinese-like Chinese.
It’s too easy to learn a version of your target language that is twisted by your base language. Many English speakers try to learn an English-centered Japanese. Many Japanese speakers try to learn a Japanese-centered English. I have had this desire myself — you want to use that word you have in your language in that other language, right? Guess what? It won’t work. The target language has its own way of expressing meaning and feeling; quite often, it may not even have a word equivalent to the word you are wanting to express. The immersion environment can help you let go of that desire to force your base language’s patterns onto your target language, by constantly showing you how the target language is really used.