I find the doubters like yourself rediculous. Have you never emersed yourself in anything? Things that seem impossible aren't remotely when you take them seriously and let them consume your every thought. Focus 8 hours a day on memorizing the digit of pi, reading music, speed reading, multiplying four digit numbers in your head, "counting cards" in Blackjack, playing chess without sight of a board, learning JavaScript, playin Tetris, or whatever. You might find that what seems impossible now becomes second nature. You might find that taking something that is second nature to a higher level (speed-reading technical documents, reading symphonies, division in your head, beating level 41, or whatever) is doable in a few more months. Why wouldn't someone who has mastered the basics of a language, perhaps beyond the level of many native speakers in terms of grammar or vocabulary in say three or four months, not be able to reach a truly proficient level in just another month or two? The poster has devised a technique of getting to an accelerated level of learning as soon as possible. If you try, you might find you can do this, too. I won't laugh.
Not everyone has the ability or personality to be a hyperfocused genius working on a difficult task. Even if they could, it's simply doubtful that a learner would pick up everything necessary to be at C1 level in 5 months. On Chinese-Forums we have a few posters who have done intensive full-time study of Chinese using modern methods for months, and I don't believe any of them managed to achieve that level in several months. A2, B1, yes.
See this long debate about whether a guy can achieve C1 fluency in 3 months:
In the SW part of the country, the surf region, there are loads of foreigners, many of whom have been here year-round for more than a decade; still, the accent is poor, the phrasing limited, and the non-native speaker element is absolutely evident.
You may immerse yourself in everything French, but unless you start early on in life it will be exceedingly difficult to attain native speaker type fluency. Language is not just speaking phrases, being able to read literature, etc., it's also being, language is being the being of another culture.
I think you underestimate just how much there is to learn when learning a language that is very different to your own. Learning Javascript, which has a limited grammar and VERY limited vocabulary, really really doesn't compare.
