Barbarian: Live like an Icelandic outlaw, the picture you might get of a "lone wolf" viking. I think the idea of a barbarian originates from Nordic sources entirely, actually, but even in those times, no reading. If there was reading, generally it was a thing for women with some masculine exceptions.

Bard: Be a scholar, but don't be a royal and also a misfit somehow. The arts are well-respected but not normalized, so a "good" student is still someone who becomes a priest, political or architect. This is still sort of normal, except replace "priest" with "engineer" for the modern-day twist. These guys can read.

Cleric: TECHNICALLY, this is "peak performance" in medieval society for a peasant. This is sort of as royal as you can hope to be, the peak of where education can get you. Unlike the Wizard though, this is more "I finished my degree" instead of "I will never be finished!" Absolutely educated.

Druid: Culturally, Native American culture wrapped up into a person. The underlying idea is that they can sort of READ NATURE or read their own fckn crazy nebulous script that few others can decipher, but that's it. It only diverts from being outright racist by not being so clearly a stereotype anymore and being it's own standalone thing. Regardless, these guys can read, just not "the normal" language. Clerics, but foreign.

Fighter: A fighter is considered default because they sort of just... Are. The most "classic" fighter would literally be a peasant, who is normally hard at work farming, but is now instead wielding a sword. That said, they definitely can't read, no education necessary to be a farmer except labor.

Monk: Buddhist tradition that sort of transforms into ninjutsu the further removed from religion you get. Whether they can read depends on the sect, but a "factory default" Buddhist monk would be unable to. There's no reason to attach yourself like that on your journey towards nirvana, but likely enough they'd memorize certain prayers and ideosyncrasies.

Paladin: This is directly the Christian Crusader-knight culturally, but without the Barbarian-esc bloodlust and the political impact. These guys are DANGEROUS, but they're also a product of ethnocentrism: a community of peasants believe in whatever flimsy ideology SO HARD that they're not only willing to die for it but they become their own intense special army. It's like your church nominating specific strong men, giving them crazy weapons and army, and setting them loose. Even knights were sort of like this, except they could maybe be stopped-- what they have in common, though, is that neither ever needs to learn to read.

Ranger: The peasants that hunt. Literally, yeah, that's all; even in D&D this term encompasses a fuckton of possibilities, but in general, these are just the people who have any reason at all to walk away from civilization or farms, then come back without having visited another civilization. No reading, but probably more than fighters.

Rogue: This one is self-explanatory, kinda? It actually does get a little more interesting, given the historical overlap between bards and criminals-- so these guys know how to read MORE than, say, rangers or fighters, but much less than clerics. They can't read books, anyway, but anybody in mercantile or trades are more closely rogues than anything else, which relies on symbols more than actual words.

Sorcerer: The difference between Sorcerers and Wizards in past context is actually small but really important. A cleric or wizard has earned being smart, a sorcerer is more "smart by design." Mostly, this is royals, nobles and politicians, who have been born into high-class roles and can't rebuke it. These guys have been reading the longest.

Warlock: Here's our good old Pagans, wrapped up in the evil, villified mist Christianity has painted them in for countless centuries. They're "mysteriously smart" and "wild, barbaric even" and "must consort with demons" because their practices don't look Christian. These guys are the ones who chant while their elders pass around blood and flesh of a demigod to consume in weekly ritual, and even though I just described a Christian tradition, these guys do it but are EVIL. It's DARK MAGIC, but really they're just Pagans, or maybe Jewish, or maybe Rastafarian, or... Bah, whatever. Generally though, "magic" in D&D is equivalent to historic intelligence, so... Yeah, despite general peasant status, people who were LOUDLY clerics of apocryphal religions were also educated. They could read just fine.

Wizard: The scholars! This didn't mean "inventors" or "historians" for a long time, but we've had thinkers and politicians for forever. This is just those, though these guys earn it more than Sorcerers. Sorcerers were FORCED to read and don't want to, Wizards HAVE to read and consume more books by the second, the autists of their eras. These guys can read the best-- reading is even part of their description, hardly any wizard without a habit, a stick, and a book.