I’m with Dragonbones.
My partner’s English is pretty reasonable, but he makes a few slip-ups. I occasionally correct him or suggest new vocabulary because it might be useful - albeit not essential - for his job (i.e., the news industry, where occasionally he is asked to get the breaking English-written or spoken news because his English happens to be better than others’ in the studio at a particular point in time). I especially correct repeat errors and provide vocab I know might be of value or of interest.
I strongly avoid correcting anyone in public (outside of the classroom, that is - and even at school I will judge the advantageousness of correcting at any particular moment). However, I might correct him in front of a close group of friends if it was necessary for communication, in the same way that I would correct a native speaker who got the name of a book wrong. Can’t think of many times I have needed to do it though.
If most of you foreign posters out there are anything like me, you have a mix of friends - some from your home country, some from elsewhere outside of Taiwan, and some from Taiwan. And everybody in your circle has varying levels of Chinese and English. There’s probably not much reason to correct a partner’s English in social situations as others will light-heartedly make it clear if your significant other is confusing them.
For social situations and for relationships, I’d say that the message and not the grammar is important. Unless, of course, someone needs impeccable English for a job and specifically asks for constant correction.
That is not to say that I don’t love and appreciate the beauty of English and that I don’t wish my lover could understand more complicated English so that I could throw it at him and express myself more subtly. But living contentedly from day to day seems more important than making our lives together an English lesson.
I will just add, that one thing I do try to avoid is dumbing down my grammar. I have seen new arrivals in Taiwan speaking to lovers and colleagues in a way that isn’t going to help anybody. You know what I mean - when somebody says: “I go 7-11” (probably while miming it), instead of “I am going to the 7-11” (while miming it).
If you have been living abroad for long enough, you can probably judge a non-native speaker’s level easily and adjust your language without the need for mangling your own language.
But as DB said - it’s up to what your partner wants. And what you want, if learning their language.
I do like Dr. McCoy’s take, though:
Nothing like a correction mid-argument to bring out a lot of stuff that needs dealing with. 