I have watched a documentary, about incredible brain (he get a language in week), what about normal brain??
For me, it also depends on what kind of language she/he leaning..
Well, I have a friend who is Indonesian. He can chat with me fluently within 6 months. Just speaking, writing sucks.
It depends on the language.
If it's not Chineese (or another difficult language) and the person is motivated it's possible to learn in a year.
Plus if you live in the country of the language you learn you can achive your goal even sooner.
Maybe you can Google it.