The American FSI class language difficulty on the basis of how long it takes students to reach a decent level, however they define that. Essentially the further the language from one’s native languages), the longer the time required.
You’re assuming they reach the same standard as Machová and other high achieving polyglots. The latter demonstrate a high level of achievement in grammar and pronunciation. I have no idea what the standard of students on CEFR courses is like when they are certified as B2. Perhaps someone who has done a course could comment. See also comments at the end.
Many universities, probably most, will require proof of language skills from foreign applicants, and some countries require, or favour candidates with, specific language skills. Quebec province in Canada, depending on the job, may require French skills. So regardless of your opinions, many people do require such certificates.
Absolutely not. Languages are far too complex.
I said many and not more. I don’t have any figures so cannot comment on numbers.
I mean a course and tests that comply with the CEFR levels:
There’s plenty of good research, some is referenced in Make It Stick written by two psychology professors from Washington University and a professional writer. Interleaving is used in non language teaching including by many sports coaches. I find it very effective for ice skating.
There’s also some good research that suggests that language learning and production uses similar neural mechanisms to activities such as playing an instrument and ice skating. See Declarative Procedural Theory for example.
I’ve met hundreds of people who learned English as a second language. One friend arrived from Korea aged 15, and lived here 30 years. He has a noticeable accent, and cannot understand films in English despite speaking well. A Russian speaking friend has lived here 19 years and is barely intelligible in English.
You have previously acknowledged that learning methods vary in their efficiency. They also vary greatly in efficacy.
Numerous polyglots have demonstrated an ability to reach high levels in multiple second languages, both in grammar and pronunciation. I don’t know if there is any solid evidence to show that they learn any quicker than most other people, or even if they do, but I do know they use numerous useful techniques which are not used in conventional classroom based language teaching.
When I went to evening classes with several respected organisations - Institut Français and Alliance Française - the teaching was very traditional. They certainly made no attempt to teach me how to learn.
My experience of formal full time education - a degree in physics - was atrocious. I attained a top grade but I had to work ridiculously hard. They used lectures, exactly as per 100 years earlier, maybe 1,000 years earlier, which are a very inefficient way to learn. Unfortunately physics researchers think that being an expert in physics makes them expert teachers. I’ve seen the same phenomenon with native French speakers who thought they were expert French teachers.
I have since a number of very useful learning techniques, some of which I learnt from polyglots, from their videos and books. Spaced repetition is an obvious one. I use it with phrases, not words. Regular testing is a similar technique to spaced repetition. Interleaving is another useful technique that was mentioned earlier. Then there is training the ear to recognise speech by listening while reading the transcript. I found this simple technique significantly improved my ability to follow speech. Another technique is listening like a child. Simply listen to speech, focussing on words, but not translating, not trying to decode, just listen, and let the brain work on it. Then there is mindset, a so-called growth mindset as described by Professor Carol Dweck can make a significant difference to the end result, as demonstrated by research. And as for accent, there are tehniques to improve that. For example, many languages have a different timing to English, and once the student is aware of that fact, they can work on their timing and make a noticeable improvement to their speech. I had to discover by trial and error that French is syllable timed. 30 years ago some French speakers were in effect trying to explain that to me, but they didn’t know how to explain it, and I didn’t understand. I’m sure there are many other useful techniques. All too often a learner will hear a difference, but they need explicit tuition to allow them to realise that difference for themselves.