Learning a human language is not "hard" in the way that rocket science is "hard". Almost anyone can learn a language and many of the least smart people in the world are adept in at least one human language. That might be obvious. We all speak at least one language because we learned it in childhood.
What's less obvious is that learning a second language is not "harder" than learning a first language -- at least in the way that learning rocket science is "harder" than learning a card game. Language is not difficult. It's has evolved in the way that it has precisely because that's the way we think already.
However, learning a human language is "hard" in that human languages are huge. Normal adult proficiency for a college graduate is over 20,000 word families. There are about 1500 common grammatical structures. The combination of idiomatic phrases for a fluent speaker is mind boggling.
Learning a language is not complicated -- it's a grind. People fail to learn human languages not because they lack the ability to learn a language, but rather because they are unable or unwilling to simply put in the time and effort. It takes the average human child 12-18 years of full time study and practice to get to adult level proficiency and fluency in their first language. You can do it considerably faster for subsequent languages if you know how, but this is really the benchmark you should compare against.
Computer languages, in comparison, are "harder" to understand, but are orders of magnitude smaller. We're not talking 30% as big here, we're talking 0.01% as big. I don't think the task is in any way comparable.