We went in search of the world’s hardest language
The Economist

There is a wide variety of different ways a language can be structured, but in any discussion of the relative ‘hardness’ of different languages, it’s worth noting that there is no language in the world too hard for a toddler of almost any level of intelligence to learn. Any ordinary kid born into any linguistic environment will acquire from scratch a functional grasp of whatever language(s) they are surrounded with before they can tie their own shoelaces, without being able to read, without having any formal lessons, let alone having to put up with pointless analytical explanations of the idiosyncrasies of its grammar. If that oral learning process didn’t happen reliably, then the language wouldn’t exist, it couldn’t have evolved and survived. So there are no objectively ‘hard’ languages, only ones that are very different from the one/s you already know.