> English got decentralized starting with the Age of Sail, but the lack of correspondence between written and oral forms is systemic and older than that.
That's not really true -- there is and was a great deal of dialect diversity within England itself. It was widespread printing that allowed languages to be standardized at the scale of nation-states in the first place: the divergences that developed after the age of sail were reversing convergence that had only begun a couple of hundred years earlier.
And although versions of English from the south and east of England became the basis for modern standard English, other dialects persisted and sometimes spread around the world, so some of the differences between English dialects globally are due to disparate influences from different dialects originating within the British Isles.
That's not really true -- there is and was a great deal of dialect diversity within England itself. It was widespread printing that allowed languages to be standardized at the scale of nation-states in the first place: the divergences that developed after the age of sail were reversing convergence that had only begun a couple of hundred years earlier.
And although versions of English from the south and east of England became the basis for modern standard English, other dialects persisted and sometimes spread around the world, so some of the differences between English dialects globally are due to disparate influences from different dialects originating within the British Isles.