[steven]

This is a cool topic. I'll try to share some of my feelings here.

On correcting/being corrected constantly:
There are particular ways of going about this. Sometimes you can ruin a conversation by being too blunt or by having bad timing. I think it's key to use what I think is referred to as something like the "mother & child" relationship. Basically you kind of repeat what they said but in the correct way. This, of course requires a certain level of ability on their part. As switching "you's" with "I's" would be important. Even still though, overdoing that can be a problem so unless explicitly asked to do so I think it's wise to pick and choose.

Relating to the "mother & child" relationship, the native speaker obviously has experience with this as their "mother" (or equivalent) did so for them. However, a person who is learning the language as their second+ language will probably make mistakes that do not resemble mistakes of a native learner. So a lot of the mistakes can be difficult to explain. For example, in English we say "go to bed, go to the mall, go to work, and go shopping". We know that "just because". When a person says "go to shopping" we have to explain to them why you need a "to". For someone who is really into their language's grammar, they'll be able to explain that immediately. For someone who doesn't think about grammar a lot it might not be obvious. Furthermore, it might be hard for the learner to grasp the concept as their language's equivalent phrase is clearly "go to shopping". Also there are dialects that can make this issue even harder-- I guess in England you guys say "go to hospital". In California everyone says "go to the hospital"... and taking away the "the" would be felt as incorrect. In other words, the learner may have had input from different dialects, which may or may not have different grammar from your own.

As for my personal experience, I've found that my version of "interlanguage" is great. You, as a learner of Japanese will try your best to use Japanese grammatical patterns and as many Japanese words as you know. You fill in the blanks with English. Your partner will do the opposite, in the same fashion. You can create that "mother & child" relationship I was talking about. It worked great for me and has worked well for other people. It requires willing participants who take it seriously. People listening in on your conversations will have NO idea what you are talking about, so it's a language that has very limited usage, but I believe it is the bridge from L1 to L2.

Referring to Japanese reluctance to interfere-- I know my wife doesn't like correcting my Japanese because she feels that what little mistakes/idiosyncrasies I have left are cute for whatever reason. We speak Japanese and pretty much only Japanese. This is to the extent that if I speak English in front of her or make a mistake in Japanese that is non-native like, she usually gets surprised because she suddenly remembers I am a foreigner!

At any rate, good luck in your learning.