I'm still struggling with English, which is my second language...
I've lived in Norway my whole life, but I could actually read and understand English (but not speak it!) before I started school, because I had some Norwegian/English educational children's books, so when I was in London just 5 years old in 1975, I understood most of what was said to me, but answered in Norwegian (to everyone's confusion

).
Since then I've had English in school for ~10 years plus a college course in Technical English for Engineers, and for the last 12 years or so, almost all the literature I've read have been in English, and - of course - I've posted the odd post here at MR, but I still struggle with quite a few things (and thanks to the holy makers of computers for spell checkers

).
And then there's speaking English... I was recently in England for the first time in years, and apart form one university course with an English teacher I haven't really spoken English since 1994, the last time I was in England, i.e. before I really started reading English and a long time before I started posting here. I quickly noticed that, even though my vocabulary has improved over the last 12 years, my ability to actually pronounce all those (new) words hasn't. And more than once I got stuck on (relatively easy) words that I can write but, apparently, not speak...
So, to become really fluent in English, I think I would have to stay/live in an English speaking country for quite some time... How long? I have no idea...
Anyway, with language (as with most things, but especially language) I think there's always more to learn, that goes for both first and second language. I know that there's a lot I can get better at in Norwegian, just as my English skills has a lot of room for improvement... (and don't even get me started on my third language, German, which I'm
extremely bad at).