The definite article Codex is a book written many times, with many variations in the attempts, all assumed to gain secret knowledge from a single ancient document. We will learn more over the course of the story.
If something buds, it’s doing alright — slang contemporaneous with Sonia’s parent’s time.
The G and K sounds in Lore family languages have a close relationship, and are represented by the same character: G, so accents may sound like harder or softer variations to the listener. Since Old Lore refers to the faerie world as Gaia and New Ancient Lore calls it Kaian, the Old Lore accent can be said to have “leaked in” to zer pronunciation here.