...and written vernaculars, whether they are Romance, Germanic or Celtic, are marginal at best.
Given the low rates of literacy in Medieval Europe, combined with, among the small literate minority (especially Church personnel), the widespread use of written and spoken latin, is there any way the niche for Romance and Germanic literary vernaculars could be squeezed out, leaving written forms of modern West European languages insignificant in modern times?
In the 6th, 7th, 8th, 9th, 10th or 11th centuries, in any given territory like England, France, the HRE, Italy or Spain, did the number of people who could read and write a local vernacular exceed the number who could read and write Latin? And if so, by how much?