For me (a Czech person) Polish is like Czech with a ridiculously funny accent, lots of different words, but a very familiar structure.
Estonian or Finnish are totally alien, I wouldn't be able to tell whether a speech was about today's breakfast or a declaration of war.
What I find fascinating about Slavic languages is that I can speak Polish in Slovakia*, get responses in Slovak and mostly understand each other. It has basically zero chance of success in the Czech Republic to the point where it's easier to find an English speaker. I speak neither Czech nor Slovak and I cannot really distinguish them but I had this experience multiple times. In written form, both are similarly understandable to me (I can get the gist and guess the rest).
* the caveat about szukanie czegoś do picia still applies though.
i'd call slovak a "middle-slavic" language, the phonetics and the lexicon makes is easy for the other slavic spekers to understand
say, i can communicate with slovaks in ukrainian and there are no significant issues with understanding too. strangely, it doesn't work for czech. at all.
https://en.wikipedia.org/wiki/The_Chinese_Language:_Fact_and...
https://en.wikipedia.org/wiki/Pseudo-Chinese theres even kind of a leet-like thing in japan to spell japanese sentences with only kanji so they look chinese
and the funniest part? the chinese themselves can actually somewhat understand these sentences
After enough time, I don't think picking up Japanese was "hard" per say, just very time-consuming. The thing with languages is that a lot of text written in modern times was not written with the intent of being difficult to understand; there are just a lot of words to choose from to get a specific point across, so you have to learn them all. Even texts that contain a lot of uncommonly used terminology boil down to learning the words you haven't ever encountered in 5 years of practice.
The main roadblock I encountered learning Japanese was not knowing the characters and common grammatical patterns to anchor yourself with that are second nature to people that know the language. With enough practice, there are plenty of times that I'm not even conscious of the effort it took to understand a different language when consuming foreign media. It's a weird feeling when you stop taking it for granted for a moment.
Also "hard" is difficult to quantify. Humans are odd and quirky, and so are the languages they create (with perhaps the exception of conlangs like Esperanto or computer languages, but even those inherit the idiosyncrasies of their creators - Perl is a good example). Every language has its weird and difficult aspects, some more than others.
Japanese is "hard" because it has a complex writing system, but (for an English speaker) the pronunciation and grammar aren't particularly difficult: in fact I'd argue that Japanese is probably easier to learn to pronounce for an Anglophone than, say, French, and the verbs are considerably easier too. And a Japanese speaker would have an advantage in understanding Chinese characters, even though the languages have no kinship. Having once taught English, I'd say it's no cakewalk either, even for speakers of other Germanic languages: the spelling system barely deserves the name "system" and English verbal phrases are downright weird (put up with == "tolerate"? How?).