Again, the ideas about language learning cross from the academic to the popular. The author starts his musings by saying “I’m not a linguistics expert at all. Just interested in the subject.” This is a convenient way to avoid any serious study of the subject.
Several studies about language-learning have been done, and the most important factor in all of them is aptitude, not the language being studied. There is no “easy” language for anyone, nor is there a particular one for speakers of any specific language. There are arguments for and against language-learning being based aptitude, but if the language being learned is Arabic, or Japanese, then what explains an English speaker being able to learn those languages other than aptitude?
The article also says “This list doesn’t include creoles, pidgins…” but then lists Lingua Franca Nova, which has been outright stated to be based on romance language creoles.
The number of lists for “language by difficulty” are numerous and mostly homogenous. What stands out is the lack of awareness that these actually discourage people from attempting to learn. Also, there could well be a political-boogey-man aspect considering that Chinese, Arabic, and Korean are each languages spoken by financial and military foes of the Western World at large.
There have been discussions in various realms of the web that one possible reason for the usual suspects being thought of as “difficult” may be that they employ wildly different forms of writing, specifically Chinese Hanzi, Korean Hangul, etc. This seems suspect as many of the “mid-tier” languages also employ abugidas and horrifically complex spelling (think Czech, Albanian), or the very same writing systems as the most difficult languages, for example Persian, Hindi, Thai, etc.
It is still widely understood that the best way to learn a language may in fact be to immerse oneself in that culture, with native speakers. Short of that, it takes dedication, a disciplined study routine, and knowledge beyond what a smart phone app can give you…say a few books on grammar.
No language is any more difficult (or easy) to learn than any other. This article does nothing to help that understanding, but is harmless enough.