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.

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.