Also, as an alternative, what's a language that took you longest (but you managed to learn it eventually)? :)
What's the shortest it took you to learn a language?
This poll will run forever.
It depends on what you mean by "learning a language", but I reached B1 in French in a bit less than a year. I've had it on a slow maintenance program since then, and it's crept up to a low B2 over the course of about 7 additional years. My longest in years was Spanish; maybe 30 years. Of course the question takes on a whole different flavor if you interpret the questions as "how many hours?" Shortest French, longest Japanese in that case.
I'm reading the Malazan Book of the Fallen.
Personally, I don't count languages stuck in A levels. For languages in which I managed to pass the A threshold, I'd estimate it took about 1.5 yrs to gain functional proficiency in Vietnamese. Indonesian took about 2 years.