Frankly, people do not have the time to deeply research this topic. You want to learn French or Spanish for fun. Duolingo claims that it can help you. So you join, try for a few days and give up.
This happened to me about ten years ago.
I too had not bothered to understand pedagogy. It is only when I wanted to learn Sanskrit, and struggled with it, that I got pissed off at the lack of progress and began looking around. There are some people on YT who talk about this stuff:
- Alexander Argüelles
- Steve Kaufmann
- Luke Ranieri
I might be missing a few others.
You first have to know what your problem is, before you can solve it.
> no one needs to discuss their phD dissertation in 4 different languages
True. In culturally homogeneous countries, you don't need four languages to make yourself understood.
It becomes somewhat necessary in places like mine where different groups of acquaintances/relatives/friends speak different languages and finding a single language at the intersection of those groups can be hard.