I read a blog entry entitled Learn Any Language in 6 Months.
One of the key components is immersing yourself in the language: listening to the language on YouTube, reading newspapers, etc.
So I guess he's not really saying "Learn any language in six months", but "Learn any major language in six months - one which has enough material available easily that you can consume lots of it".
For example, I think I'd have a tough time finding significant content in Inuktitut: audio is the most problematical, but even written is probably tough if I don't want to read the minutes of parliamentary meetings or government brochures on avoiding AIDS. And even Romansh would be tricky: quite a few books, but I'm not sure whether I could get audio (RTR is mostly music, for example).
So, yeah. Good for you if the language you want to learn is Japanese. But something like Walloon? Is tougher.