To me it has two entirely different meanings and I am not sure which is correct.
1st possible meaning: The use of English is prevalent in not just English-Speaking countries but also in non-English-speaking countries.
2nd possible meaning: The use of English has become inevitably common in English-speaking countries.
The first meaning makes more sense to me, but the second one is proposed in the book as the rightful translation.
I saw this sentence somewhere in a book alone, which means there was no sentence before or after to elaborate the author's intention. The book was explaining the meaning of the word "endemic", which as far as I know means prevalent, native and indigenous.
Edit: Or probably a third meaning would be: The use of English in terms of its origin is not native to today's English-speaking countries