It's got a Germanic base, a French upper layer, Greek and Latin for academic terms, Norse and Celtic stuff left over from ancient times, and then truckloads of vocabulary from its international presence and usage. The rules are tricky. It's also got the third-worst orthography in the world (Scottish Gaelic and Classical Tibetan are worse). I heard a linguist in Ghana say this. In learning to write it, there are certain similarities to learning Chinese: you just have to memorize a lot of it. There are some rules that can help you figure out some things if you go deep into it, but you just have to start with memorizing.

English is not difficult But once you get into an advanced level it gets really hard to gain advanced vocabulary items