Readers of Terry Pratchett have to understand that he, and most of his characters, speak British English (of some variety or other), including idioms and creative spelling for dialect and other forms. It's part of the charm of his books, which I think are the best
novels in English since Dickens, and the funniest since Mark Twain. Or vice versa.
Pratchett is probably my favorite author, because his treatment of language (and the people who speak it) demonstrates that he gets it.
In fact, he got it a long time ago. Witness the Latin mottos of Unseen University:
Nunc Id Vides Nunc Ne Vides
or of the city -- and state -- of Ankh-Morpork, where Business is King:
Quanti Canicula Ille In Fenestra
Not to mention the Greengrocer's Apos'trophy which appears misplaced in every piece of dialog uttered by his greengrocer characters. The joke is, of course, that apostrophes are inaudible in speech, so nobody listening can tell where they are -- but the writer, and then the reader, can.