It has become pervasive, though, hasn’t it? One recent book on Tolkien, in which a number of international contributors were given a voice, bemoaned “the fact that English has, without a doubt, become the koiné in Tolkien studies – some sort of Middle-earth Common Speech” . And of course, English has spread far beyond Middle-earth. It is spoken in almost every corner of the world, and learning it is frequently required in the educational systems of many countries. I am told that Indians begin learning English in school at the age of two years! (In the U.S., children don’t even begin school until age five or six!)
Why has English become so popular? I won’t rehearse the many arguments about the whilom successes of the British Empire, the emergence of the United States as a world-dominating political and economic force, etc., etc. You have heard these arguments many times. But other answers might be closer to the mark — or at least equally valid. Why, after all, didn’t Chinese or Hindi become the ascendant lingua franca? Both can boast more native speakers than English, almost as widely distributed around the globe.
Part of the answer might be the particular structural, phono-logical, morphological, and assimilative qualities of English. All the foregoing has been a perhaps too lengthy introduction to the following quotation. Here, Richard Carew (quoted in William Camden’s Remains Concerning Britain) extoled the virtues of English some 400 years ago. His description of the “excellency” of the English language seems to come near the mark (bracketed insertions are mine):
The Italian is pleasant, but without sinews, as a still fleeting water. The French, delicate, but even nice as a woman, scarce daring to open her lips for fear or marring her countenance. The Spanish, majestical, but fulsome, running too much on the O, and terrible like the devil in a play. The Dutch [i.e., modern German, not modern Dutch], manlike, but withal very harsh, as one ready at every word to pick a quarrel. Now we, in borrowing from them, give the strength of consonants to the Italian, the full sound of words to the French, the variety of terminations to the Spanish, and the mollifying of more vowels to the Dutch, and so (like Bees) gather the honey of their good properties and leave the dregs to themselves. And thus when substantialness combineth with delightful-ness, fulness with fineness, seemliness with portliness, and currantness [i.e., fluency] with stayedness, how can the language which consisteth of all these sound other than most full of sweetness?Carew goes on from here to provide a litany of Classical writers and the English writers who capture their styles in that language. I won’t repeat them all here. He’s clearly very partial to English (“if mine own eyes be not blinded by affection,” he admits), and he may go too far in some of his verdicts — but even so, I think he has hit on some important points. Most importantly: that even then, and moreso now, English owes much of her success (and, to Carew, aesthetic virtue) to her unique ability to assimilate the most successful or euphonic words and elements from other languages and to make them her own.
Again, the long words that we borrow [e.g., from the Latin and Greek], being intermingled with the short of our own store, make up a perfect harmony; by culling from out which mixture (with judgment) you may frame your speech according to the matter you must work on, majestical, pleasant, delicate, or manly, more or less, in what sort you please. Adde hereunto, that whatsoever grace any other language carrieth in verse or prose, in Tropes or Metaphors, in Ecchoes [i.e., onomatopoeia] and Agnominations [i.e., alliteration], they may all be lively and exactly represented in ours. 
I welcome your thoughts on this — especially those of you whose “cradle-tongue” is not English. (And let me congratulate you for reading this blog in English and perhaps helping to prove the point. ;)
 Tolkien, J.R.R. “English and Welsh.” The Monsters and the Critics and Other Essays. London: George Allen & Unwin, 1983, p. 190.
 All quotations, loc.cit.
 Segura, Eduardo and Thomas Honegger, eds. Myth and Magic: Art according to the Inklings. Zurich: Walking Tree Publishers, 2007, p. ii.
 Camden, William. “The Excellency of the English Tongue, by R.C. [Richard Carew] of Anthony Esquire to W.C. [William Camden].” Remains Concerning Britain. London: John Russell Smith, 1870, pp. 50–1. The text quoted is the 1870 reprint of the 7th edition (1674). The last edition Camden himself revised was the 5th (1607); the first edition appeared in 1586.