Pretty much everybody has a hard time grasping English, even other speakers of Indo-European languages.
All languages pick up loanwords from other languages, but English has a couple of... special... habits as far as this is concerned. Loanwords are perhaps the toughest: all languages pick up words from other languages when they come into contact, but most languages adapt the spelling and surrounding grammar into their own systems. English doesn't normally do that: it preserves the original spelling and often the original grammar, which sounds great until you realize that now you've just grafted a new set of rules into the English language for this particular situation.
That's where a lot of the complexity of English really comes from. It's actually a lot more regular than many people think, but at any given time it can work according to any of a staggering number of different rulesets, and to know which ruleset you need to use, you have to know which languages your words are coming from, which English doesn't really have a way of encoding, and very few people, even among teachers of the language, actually know what all of the rulesets are, so you probably don't know them all either (nor do I).
It's like playing Mao with words.