[imtringued]

My experience is that this takes an absurd amount of time to learn anything. Sure you can probably learn Japanese in one year by staying in Japan but only because you have effectively spent 5000 hours doing nothing but Japanese. My learning efforts haven't even scratched 10% of that yet I am much further along the journey than 10%. My own estimate would be that I'm 50% the way to fluency.

If it works for you then fine, but it doesn't work for me.