The world's three most widely spoken languages appear to be Mandarin Chinese (>10 hundred million), English (5 hundred million) and Spanish (3 hundred million).
Excellent things are of course written in Mandarin and Spanish. But due to the unequal global distribution of wealth, far fewer books must be written per capita in either of these languages each year than in English.
Conversely, it seems unlikely that any of the world's smaller-but-still-big languages, French for instance, would exist under such socio-politic conditions that its speakers produce more books per capita than the English-speakers.
So most of the good books that appear globally every year are written in English. But as we all know, good ones are rare. Most books written in any language are crap.
[More blog entries about books, language, English; böcker, språk, engelska.]