English books are translated worldwide, but it is very hard for a non-English author to be known in USA and UK so that his/her book is translated to English. You must already be REALLY famous in your country to be translated in English.
On the other hand, for an author, to translate his/her books in English is quite expensive. A good translation, which can compete in terms of quality with books written directly in English, can cost up to 3,000 euro. Writing directly in English is not a good idea: a foreign author will never be so confident with English to compete with native authors.
However the English market is enormous, a great opportunity, but very few foreign publishers are available to translate to English the books they published, and no USA/UK publisher is available to translate new or less know foreign authors, even if book is very good. For example, in Italy, selling 10,000 copies of an essays or 50,000 copies of a nove is a BIG success. How many people outside Italy knows Italian? Really few.
So the problem is that Italian authors are not known outside Italy unless you consider very famous authors as Calvino or Eco. The real problem is to create a network to let English publishers to know and appreciate foreign authors and invest in translations.
Dario de Judicibus