I’m kinda surprised that Mandarin ends up in the hardest category in these kinds of analyses. I took it in college - 1 hr a day for 6 semesters. I’ve never been fluent, but I could hold a decent conversation and muddle my way through a newspaper. Pronunciation is hard, but can be taught effectively in about a month, maybe two (the minority of students who didn’t get it by then, still didn’t years later). Grammatically, it is much, much simpler than the others on the list. No inflections for anything. It’s mostly syntactic algebra.
Reading and writing are hard, because you need to memorize thousands of characters, so maybe that’s what they’re talking about. But I learned (and have since forgotten, but it has been 10 years) over 2000 characters in a grand total of less than 400 hours classroom time, maybe 600 hours total study time, so I have to wonder how much they expect people to learn that takes 2200 hours? I also know two people who are in the foreign service, as Mandarin speakers, with less than half that much instruction.
