I wish people like this would present their proficiency levels in a more accurate and less spectacular way. Many people can do what this person has done if they put in the hours -- there is no magic to it. Some comments:

- The word "fluent" can mean almost anything. The CEFRL (https://en.m.wikipedia.org/wiki/Common_European_Framework_of...) gives a much more useful frame of reference, one that I will use here.

- The B2 level is where one can interact with native speakers and native texts "without strain". It takes about 600 hours of study for languages like Spanish or French, and a bit more than twice that for linguistically distant languages like Korean or Arabic.

- My guess is that he is at B2 or higher in very few languages. Based on the YT video (https://www.youtube.com/watch?v=Oudgdh6tl00), he meets that criteria in English, Korean (he lived there for many years), and French (not sure, but it's not that hard for English speakers). Maybe that's it. You may not know it, but there are tons of people who already have done this in any reasonably sized city in the US.

- The rest seem to be all low level or very low level skill development. The tasks he talks about would be routine in university level courses maybe up to the third year, but mostly first and second year. This is roughly CEFRL A1 to B1 -- not terribly impressive. Just put in the time (roughly 100 hours for A1, 200 for A2, and 400 for B1). Basically what he can do is stuff like a basic self-introduction, simple information exchange on routine matters, read some signs, etc. No newspapers, no radio, no TV, no work that requires communicative skills. At best, this would be like an enlightened tourist level.

- On a related note, I was a bit disappointed in how little time he spent on fluency-level tasks rather than memorization or drills.

- Once a person learns one language, often times many other languages become much easier to learn. For example, learn Spanish, and Portuguese and Italian become much easier (especially listening and reading) since there is so much overlap. His knowledge of Korean helps him with Chinese and Japanese since he learned the Chinese characters as well as the Chinese loan words, many of which are shared in some form across all three languages. Dutch/Danish, Hindi/Urdu -- the list goes on. He mentions this slightly in the YT video, but I think many people don't appeciate how much the overlap can be. As a simple example, I knew a very talented language learner who was able to score CEFRL B2 on a French reading and listening test just based on her high level (C2?) knowledge of Spanish (both are Romance languages). She is exceptional, but it's doable.

- With a good teacher/advisor, most educated people can reach the level this guy is in most of the languages he claims to "speak" or be "fluent" in. The challenging part of language learning starts at B2 and comes to a head at C1 and C2. This is distinctly not a level that most people can reach if they put in enough time. To reach these levels requires a great deal of linguistic and cultural empathy and self-awareness that most people don't have.

This is an area I have quite a bit of theoretical and practical knowledge of. Please feel free to ask any questions and I will do my best to answer.