I'm married to an immigrant whose first language is Chinese (she speaks three different Chinese languages) and English still drives her nuts at times even after living in Canada for 25 years and having me as a partner for 23 of them. We have way too many screwball exceptions (as that poem points out). It doesn't help that the Chinese (at least in Mandarin and Shanghainese, can't speak for all of the languages in that family) don't have the concept of masculine and feminine third person pronouns so that she's always messing up "he" and "she".
English Grammar is the hardest to learn because we make everything complicated..... For instance "I know" Silent K......... Stupid luckily I grew up with it so I except it now....
Is English hard to learn? I think that's a myth. I have a lot of friends in Europe who don't have English as their first language but speak English fluently. I agree that English is hard to pronounce correctly but to learn to at least to competent level is quite straight forward.
Have a go at Finnish or Hungarian and then come back and say English is hard to learn!
Danielle x