Spellbound / Blake Charlton.

Enhanced descriptions from Syndetics:

In a world where one's magical prowess is determined by one's skill with words and ability to spell, Nicodemus is a wizardly apprentice afflicted by a curse that causes him to misspell magical texts. Now, the demon who cursed him has hatched a conspiracy to force Nicodemus to change language and ultimately use it to destroy all human life. As Nico tries to thwart the demon's plan, he faces challenges from all sides. But his biggest challenge is his own disability, which causes him to create chaos wherever he goes. And the chaos surrounding Nico is affecting the world so profoundly that the kingdom to which he has fled to gather strength is on the brink of civil war, and he suspects that his closest allies--even Francesca, whom he loves more than life itself--may be subject to the demon's vast powers. As Nico tries to forestall the apocalypse, he realizes that he doesn't know if he can fully trust anyone, not even the woman he loves. And if he makes one wrong move, not only will hislife be forfeit, he may end up destroying all mortal life as well.Introducing new twists to the unique magical system of Spellwright , and exploring issues that will bring readers a deeper appreciation of a fascinating world, Spellbound is sure to please Blake Charlton's fans and increase their number.
Spellbound is a Kirkus Reviews Best of 2011 Science Fiction & Fantasy title.