Every time I hear this question is a facepalm moment. It’s so difficult to answer because it’s always subject to how you define “fluent” and so “fluency” isn’t a yes-no sort of question. Therefore I always respond with an awkward “Urmm, well, maybe, depends what you mean…”.
I suppose I should first say how I view my level of Chinese at the moment. If there’s an idea that I want to communicate, I can do it using a fairly good range of words, although there will be times that I’m struggling to find a specialised word. For example, if I wanted to find a plumber, and didn’t know the word for ‘plumber’, I would ask if anyone knew “someone who could fix the water pipes in my house”. It communicates the idea nicely, and gets the job done, but is kind of cheating. Therefore I’d probably say that I’m confident, and I’m an expert corner-cutter, although my range of extended vocabulary probably isn’t actually that good. (‘Plumber’ is shuĭguăn’gōng 水管工, so now I know, and looking at the characters, it makes total sense: “water” + “pipe” + “work”).
This isn’t something I think is unique to Chinese. Whatever language you learn, I think that “fluency” is anything you want it to be. It might be the ability to speak simply to get a point across, to attain confidence in speaking and listening like a native, to read and understand complicated texts, or to be able to write essays or articles with native-style flair. I would say that Chinese in particular makes it hard for a foreigner to achieve this final one, since it has an insane amount of idioms and so-called “four-character expressions”, all littered with subtle nuances and historical references. It’s virtually impossible that I’ll ever be “fluent” if it’s this last definition that you mean.
I would imagine that most language learners would agree that it is a long and sometimes arduous road through tedious vocab drills and grammar exercises to finally attain some degree of confidence. Living in a totally immersive situation, like I did in China, however, creates some deceptive illusion that you can skip the ‘studying’ step, and just let it ‘all soak in’. Maybe if I were three years old, couldn’t speak any other language and didn’t live in a flat of English-speaking housemates, it could possibly have worked. Living in the country shouldn’t be seen as some magical key to fluency, and I slightly regret that I didn’t take to the whole experience more diligently.
For the moment, though, if I’m asked the “fluency” question again, I suppose I’ll have to settle for simply responding “sort of”.