On a superficial level that seems like a roughly correct ranking in my experience. On the other hand, I picked up one of the category 3 languages pretty easily. I think some of these are more "weird" to a native English speaker than "hard" per se.

The aspects that make languages difficult for a native English speaker vary quite a bit with the language. I would expect individual experiences with the languages to have high variance as a consequence.

It seems like an extremely coarse classification. Category 3 contains languages with very different degrees of difficulty, while Bulgarian and Russian are both Slavic they are nothing alike in terms of difficulty since Bulgarian is the most analytic of Slavic languages (has the less inflection). That makes it extremely easy to learn compared to Russian.

As others hsve pointed out, it's a very coarse (and rather arbitrary) categorization.

E.g. both Turkish and Russian are in Category 3, but Turkish is trivial compared to Russian.

Turkish grammar is extremely regular, and follows easily defined rules that fit about two pages of easily digestible tables.

In comparison, Russian is a separate class tought in Russian schools for four years to native Russian speakers. And you still get people who can't properly inflect numerals, for example.

Difficulty scale looks about right.

>If an English word looks similar to a Russian word, then the stress is likely on a _different_ syllable

Most of these are Latin and French loanwords where Russian (same as e.g. German) carried the accentuation over from the source language. English is the odd one out as it insists on putting the primary stress on either of the first two syllables, except in some recent loans (and they still get a secondary stress). With nouns the preference is for the first syllable. Russian surnames get similarly butchered, including notably Nabokov, which could have been adopted unchanged.

Stress pattern in russian is not just different from English, it's also different from Ukrainian half the time.

Fiendish logographic writing system (Chinese) vs fiendish grammar (Russian). I'm not a fan of Pinyin transliteration aesthetically.

Russian has a lot of words I can recognise in it. Not just loanwords either but words such as brat, dva, kot (brother, two (twa), cat). The other problem is the tonal system although Mandarin balances that out with simple grammar. Mandarin strikes me as mostly vowels and Russian as strings of consonants.

I have been generally successful at learning Russian as an adult, but tonal languages are something that I just struggle with on a fundamental level. I want to express meaning and connotation with tones, rather than denotation. On the other hand I've never been terribly motivated to learn a tonal language, so it probably could be overcome, but it's something that would take an immense amount of training to overwrite that tone=connotation/emotion/question instinct.

It is also quite frustrating when a native speaker is completely unable to understand something you say because of a tonal issue. To their ear it must sound entirely different, yet to a non-tonal ear it sounds like you're saying everything 'almost' exactly correct.

Only somewhat related: I was surprised by how simple and sound vietnamese grammar is when read through the latin alphabet. Tones are only a problem when speaking but it's increadibly easy to start understanding signs and labels in the country. Slavic and baltic languages i can read are MUCH harder to start with.

So i kind of suspect it might also be the case for chinese: tones and the alphabet are obscuring a clean grammar.