Somehow I’ve expected you to link that video 
I am going to share my thoughts, if I may.
First of the points I agree with:
- Kids don’t learn languages faster then adults.
- It’s a good approach to study language-unrelated content via a foreign language in order to improve that. It’s also risky, though, as you have to make sure everybody can follow the content of the class. This requires a very skilled teacher.
- Interest/motivation is important. While this is definetely true it is a very general statement that applies for every subject. However, you cannot enforce this. Many students will simply not feel motivated to learn a language they don’t need in their everyday life. And some animes or similar will not necessarely change that.
Now on what I would disagree on.
First of all, even though he somehow states that a lot of what he is saying is based on personal experience, he makes quiet some general statements based on a mainly English speaker centric perspective. At least this is the impression I get.
- He starts with stating that 80% of the US and 60% of the British citizens are monolingual. What about non-English speaking countries? What about countries where several languages are spoken? Where does that 20% gap between the US and the UK come from?
- The way how he describes language teaching is taking place is in complete contrast to my own experience, but fit to the way how you and other presumable native English speakers describe how languages are or were taught to them. I talked about this in other threads but just to point out some things he mentioned in that video:
- grammar from the beginning on (just no)
- 1-2 hours per week, 5 years in total (twice to three times the hours for twice the amount of time, plus a second foreign language for 4-6 years)
- He states, that most students are not able to communicate in the language taught after school. This is only partially right. First off, he is again judging based on the English students only, and secondly he is not asking whether there could be a reason that after all there are some students that can do so, and what those reasons are. From my very own experience these are the aspects that diffentiated the not so good students from the good ones at my school:
- Native speaking skills: Students who were bad at foreign languages, may it be English or a different one, usually weren’t good at their native language either. They often had a very limited vocabulary, were using the same formulations all the time and made very basic grammar mistakes. The main reason was they generally were not very interested in anything beyond the interaction within their social group. You can’t improve your language skills if your only input comes from sources (this includes other people) that aren’t above your skill.
- Practical usage: Those who were good usually had some use case to apply the language on. For me in English it was computer games who were often in English and music. I wanted to know what the musicians were singing (or grunting, in my case
) so I had a motivation to learn.
I wouldn’t argue against the approach to language learning he talks about at the end of the video. But I disagree with his conclusion. I for one never was in a country were there is English spoken nor did I actively learn the language. I never learned vocabulary, grammar or read English books or used other means to actively practise my language skills. Music and games were really the only thing, and I started rather late with the latter. Nevertheless after leaving school I was able to understand any English text given to me, ranging from novels to scientific papers and used mainly English sources to teach myself all kinds of stuff, from programming over the way graphics engines and shaders work to what else not. And I was definetely not the best in my class.
From this I would draw two conclusions:
- It seems that there is a deficit not in the way languages are taught at schools in general but especially how it is done in the US and the UK. I’ve heard from several people who immigrated to Germany from the US and who send their children to school here that they consider the german way of teaching languages much better then the US one. That doesn’t mean that our way of doing this is optimal, it certainly isn’t, and there are surely many other countries that perform well in that regard. But it really seems to be a problem more evident in English speaking countries (we had a paper demonstrating this, too, that was linked in another discussion in this forum). At this point I would like to add that the overall motivation for a native English speaker to learn another language is probably lower then for a non English speaker to at least learn English. It is the lingua franca nowadays and therefore often a prerequisite for certain job or educational perspectives.
- There is a far spread misconcept that teaching at schools implies that it is only the school who is responsible for the process of teaching. But especially when the children get older and become teenager, it is also their responsibility. A lot of the students that perform well in English at school here in Germany do so because they consider it important to be able to learn the language and therefore they often actively try to improve their skills. One very far spread method is reading English books btw. This applies to all subjects though.