Inkspell by Cornelia Funke

From chapters.ca:
Although a year has passed, not a day goes by without Meggie thinking of Inkheart, the book whose characters became real. But for Dustfinger, the fire-eater brought into being from words, the need to return to the tale has become desperate. When he finds a crooked storyteller with the ability to read him back, Dustfinger leaves behind his young apprentice Farid and plunges into the medieval world of his past. Distraught, Farid goes in search of Meggie, and before long, both are caught inside the book, too. But the story is threatening to evolve in ways neither of them could ever have imagined.

Sequel to Inkheart
Originally in German.