TL;DR: Attempting to artificially create a human language is a complete waste of time. It's almost as wasteful as learning a natural human language you will never actually use practically.
The ops question stems from a deep misunderstanding of what human language is. Humans use language to communicate meaning. The important part here is the meaning, not the language. Language itself is practically arbitrary. Sure, there are similarities across human languages. Like, the English R sound is pretty uncommon and comes late in language acquisition. This doesn't mean that English is "hard". English isn't hard. Neither is Chinese, nor is French, nor vietnemese, nor any other natural human languages.
Different languages do not take different lengths of time to learn. Native language acquisition occurs at approximately the same rate overall across languages. Different people acquire language at different rates, but there are clear statistical trends, and there tend to be only a few commonly used learning strategies for any given problem in language space (like making the English R sound). You might think certain languages are harder to learn because they are harder for YOU to learn, but this isn't the case. Secondary language acquistion occurs as a bootstraping on an existing scaffold (your native language). That means the base language significantly affects the ease at which a secondary language will be acquired.
Language is organic. People creatively use language in order to communicate meaning, as we said above. There isn't actually a thing called "English". There is a group of people who understand each other. They play a language game, but they don't all do it the same way. You've heard of something called "dialects"? It turns out that people who can understand each other don't necessarily always play by the same rules. Rules vary, and that varience tends to corrolate with geographic distance. Now, even though they vary, people tend to still understand one another pretty well across dialects. You get to the point eventually where people no longer understand one another, even though the languages are still recently historically related (Spanish and French). At this point, we say they speak different languages. The point of this "language is organic" line is that language CHANGES. Sometimes it changes slowly, sometimes it changes rapidly. It is an absolutely critical feature of language that it can change.
Humans adapt language to serve their needs. It evolves over time, morphing into mutually unintelligible versions of itself across speakers. Now, language change does work acording to some rules. There are syntax and grammar features which human brains appear reluctant to violate, and there are common strategies which are usually followed (though there are exceptions to pretty much anything). What does language change mean? It means that if you go designing a language(an artificial language), your carefully designed language will change into something else over time (a natural human language), People will change the rules you have prescribed to suit their needs. They will invent new words. They will stop using old words and use different ones, sometimes for reasons as trivial as that they like the way the new ones sound. They will alter syntax creatively in order to express themselves, but insodoing they will make those changes acceptable over time. What, then, is the point of designing an artifical language if it is desitined to quickly change into something essentially identical than what you started out with?
The only artificial languages which persist are computer languages. They persist only because a computer is very unlike a human in that it will not attempt to parse your expression for layers of meaning. Computers demand all expressions have only one possible interpretation. This is vastly different than human language processing. If you would like an example of the utter failure of humans attempting to create artificial languages then go look up Esperanto.
IAAL and IAAPoL (I am a linguist and a philosopher of language)