|Aeneas in the Underworld (Brueghel)|
The best writers quote Latin. They pay homage to the rich language and culture which had the greatest influence on the English language, Western literature, law, mythology, grammar, and history.
Yet there are a zillion errors in Latin phrases and quotations in books.
A. S. Byatt made a mistake in her excellent novel, The Children's Book: "...pro his et omnis donis tuis." The ablative plural of omnis is omnibus. It's a third-declension adjective, not a second-declension, and, yes, the ending is -ibus, not -is.
Paul Fussell, in his clever 1980s book, Class: A Guide to the American Status System, also made a basic declension error. Latin can be about class, but sometimes even the classiest go astray.
I recently found an error in the excellent Y.A. fantasy novel, City of Bones by Cassandra Clare. (Thank you, onliners, for recommending this book.) Clare uses the phrase invictus nox ("invincible night"), but the correct form of the adjective is invicta, not invictus. The adjective modifies a feminine singular nominative noun; therefore, the correct ending is "a."
Writers of historical novels like Robert Harris (Imperium and Pompeii), Steven Saylor (Roma), and Helen Dunmore (Counting the Stars) are very careful about their Latin quotes.
Margaret Drabble is also an excellent Latinist. The heroine of her wonderful novel, The Seven Sisters, respects Latin and refuses to teach it even as a sub because she knows she's not qualified. Candida is a student of The Aeneid who feels drawn to Virgil's underworld (Book VI). Drabble doesn't mess around with the Latin any more than her heroine does.