So far no one has noted the lamentable obverse of the OPs observation. If English is the most difficult language in the world, why are native English speakers not rushing to learn all these easy languages.
I have attempted to learn - and failed in each instance - Norwegian, Finnish, Russian, German, Danish, Dutch, French, Italian, Spanish, Indonesian, Malay and Manadarin. My single succes in language learning came when I lived in Cairo: I resolved that, following the aforementioned failures, I would make no attempt to learn Arabic. When I left four years later I had attained my goal.
I do have an interesting measure of language difficulty, based upon the amount of alcohol one has to consume to think one is speaking the language. Thus Spanish is a two pint of lager, language; Fench is three pints. Chinese requires two bottles of Jack Daniels over a thirty six hour period and may therefore prove fatal for some individuals.