That's an interesting point to ponder. In France, there are constant calls to spelling reform and such. Of course, spelling and grammar as they are are incredibly annoying and backwards, but anyone with good command of them can read any text as far back as Rabelais (writing around 1510), and even Middle-Age French such as Villehardouin (writing before 1200) is perfectly readable with some effort (I've done it, without having more than 2 courses in Ancient French, back in the 80s -- you at least need to know that there are declensions, with 2 cases, and how they work -- OK, knowing some Latin definitely helps too :) ), it's getting really difficult IMO only with _Les quatre fils Aymon_ ( https://en.wikipedia.org/wiki/The_Four_Sons_of_Aymon ) and prior works (roughly before 1100).