The simpliest language in the world is Chinese. 1.5 billion of chinese speak it without accent ... )))))

I imagine that's hard for some people to pronounce the sound "Ы" и "Щ"). 

Learning a different paradigm of grammar, ex. learning to think in terms of three genders and six cases. Learning about hard and soft consonants, learning that articles are not necessary, learning that there are only three tenses and two aspects. In English we have twelve tenses. For example, in English I think of the perfect as the default mood and use the imperfect when necessary, it seems to be in reverse in Russian. Speaking two romance languages, the adjective endings tend to match the endings of the nouns -- this is not the case with Russian as the adjectives only match in case, but not ending, also getting used to the fact that in adjectives, there are only singular genders and plurals are all bunched into one. I think all of these ideas are vital before even starting to learn too deeply because without understanding these differences it makes it really hard

I would say pronouncing “o” as “o” or “a” is the most confusing part 😅😅 until now