Also....Why would many in an agrarian society need to be able to fluently write? Even needing to sign their name would likely be a rare event. It is entirely possible for a person to be able to read and not be able to, or be comfortable with writing.
Exactly. That's why Gutenberg's invention of the Bible had nothing to do with literacy. It's a Protestant myth. Reading and writing had to do with the development of the cities and the trade boom in the 17th and 18th centuries, peaking with industrialization (19th century); literacy is tied tro social and economic factors, independent of Christianity.
In the East, Greeks were always urged to read and know their scriptures by their hierarchs because Greek scriptures were written in the Greek vernacular (koine) and not some unintelligible language.
Franks and Goths were Germans and their language was alien to Latin. The only reason they used Latin is because their language was too primitive to use for prose. Before the Norman conquest, in England the only written language was Latin.
In the east the Bible was translated into Church Slavonic which was derived from the Old Slavonic vernacular, understood by everyone, even the illiterate. In addition to that, for the illiterate the Church used iconsthe Bible, a pictorial bible of sorts. That way even the illiterate knew how to "read" the Bible.
In the West, the vernaculars were not sophisticated enough for writing. It was Luther who, through the translation of the bible actually created modern literary German language fit for prose. And even then, such a language was not sophisticated enough for science. So, Latin was a must for any scientific and academic work. Even Luther wrote in Latin.
The Church ahd nothing to do with that. Some countries, like Croatia, used Latin in their Parliament until 1840 simply because the native language wasn't developed enough. In England, the language of the court and the middle class was unintelligible to the Cockney-speaking illiterate masses. That's why "literacy" was defined simply as being able to "sign your name" and nothing more than that. It didn't mean you can read and write.
Out of context, it is easy to make a false conclusion that you had Cockney-speaking masses reading and studying the Bible just because 50% of the population could sign their name!
To be truly literate you need education, and to get education you need money, one thing most people didn't have (imagine that!), especially because they had loads of children that had to beg and steal, or they worked on the farm from the youngest days from dawn until dusk and had no time to study.
If they couldn't make the ends meet, who had the time and the luxury to study, and the money to afford a Bible? Easy, the educated, not the masses. So, this myth about how Christianity led to literacy after the printing press, and how it liberated the slaves is as bogus as a three dollar bill.