On a related note, I recently heard the bizarre-sounding statistic that in early 19thc France, 80% of the population didn't speak 'French'! I doubt it would be that high, but the rural/peasant populations of the 18thc probably didn't speak a version of the language that the educated/Parisian upper/middle classes could understand! I suppose they would be speaking dialect, Occitan, patois, etc. as a first language, much as large areas of Britain in the same period spoke Welsh, Cornish, Gaelic, rather than the South-East middle-class English which is now the 'standard' language.