One issue is that often it takes someone who has had language instruction experience to properly explain nuances. I've often asked my spouse questions about grammar usage, and since it is instinctive for her and not a premeditated decision like it is for me, she is unable to clearly delineate the proper context and edge cases where a certain grammar would apply. Same with vocabulary. When you have a dozen synonyms, each with a different nuance, it's often tedious and difficult for a non-language instructor to provide clear explanations.
I think it's best to use native speakers as oracles: you can give them a piece of language and they can tell you if it's correct/natural or how they'd phrase it. You can't expect people to go beyond that, and trying to explicitly systematize the grammar isn't necessarily important or that valuable anyway; you need to internalize the grammar (as one has done with a native language) and that's not a conscious process.
I think this really depends on the individual learning style. Some people are able to extrapolate from examples and internalize it (e.g. those people who learn language simply from watching TV), and others need a more explicit structure to guide them before they really start internalizing. No method works for everyone all the time.
Yeah, I talked to a lot of couples and am totally aware it's hard to explain your own language or teach a language if you're not a teacher.
I actually even know cases where language teachers that failed to teach their own language to their partner.
So I'm more gearing it for having your partner act as support, practice, clarification, and reinforcement along with prescribed self-study. And also just make it fun!
What pitfalls did you run into? From what I heard, the learner often expects the other person to become their personal on-demand language teacher. And then patience burns out quickly. I think it works if the learner is committed to self-study but only relies on others for a bit of reinforcement, clarification, and practice.
