A Thing of Vikings (HTTYD/Disney's Mulan/the 11th century), Chapter 160: Frameworks and Foundations.
https://archiveofourown.org/works/104089.../146920855
An Introduction To Dragon Biology, 17th Edition, Oxford University Press, 1793, Wrote:Literacy spread rapidly through the draconic population in the 1040s to 1070s, reaching effectively worldwide distribution by the 1100s, barring political and social resistance to its adoption, both from human sources (wishing to keep their dragons illiterate) and from draconic sources (viewing writing as a tainted human innovation). However, contrary to the beliefs of certain ideologues, dragons are not as well-adapted to writing or reading as humans are, simply as a matter of biological fact. Many draconic breeds lack the fine motor capacity to be able to write at all (although this changed with the coming of typewriters), and limitations on draconic cognition likewise puts an upper ceiling on their reading and writing skills. Even the most accomplished literate dragon recorded, the Night Fury Reckless (NF-00009371-b), had an expressive written vocabulary of approximately 16,000 words, which is only half that of a typical adult human native speaker (between 20,000 and 35,000 words). Meanwhile, most dragons typically top out at an expressive vocabulary of 3,000 words, and a receptive reading vocabulary of 6,000-10,000. While this is more than sufficient for day to day use in our society, most dragons are simply limited to the same degree as a human child when it comes to reading comprehension and composition.
https://archiveofourown.org/works/104089.../146920855