"It's in Latin," Percy explained patiently. "The same language most of our spells come from."
...that being said, Percy still wasn't sure what they said, as he didn't know Latin.
Still, to keep from looking too stupid, he straightened up, peered at the plaque. "Oh, look, they've translations. The one on top says "'The devotion of Abbot Peter and his gentle flock gave me to the Church of St Peter of Gloucester.'"