Mark Liberman:

it’s seriously bad luck for the human species that English happened to hit the linguistic jackpot… The problem is the way that English is written, which is really, really hard to learn, in comparison to most other languages with an alphabetic writing system.

Most of my friends and colleagues these days are non-native speakers, and several strongly insist that English is a very simple language. The paper Liberman cites provides empirical evidence that it is a tricky language by some measures.

Chart of error rates for a particular test performed across a range of languages