The article misses emphasizing or properly mention English's success started not in conquering but overcoming conquerors.
It's hard to think of English as having a single source, as what remains of that gets very small as you go back in time. The language in England and thereabouts overcame several invasions. Roman, Viking, a couple of invasions you'd call French now, among others... they all left their mark, or more accurately the native population absorbed a sizable portion of the invaders' language and established and re-established the dominance of the English language in the area.
If you take a beginners' course in French you'll probably get the line that English is 60% French, badly pronounced and it's true! (more or less)
It would sure be hard to standardize something that has a habit of repeatedly bolting on large chunks of other languages, nevermind it's modern regional inconsistencies.