1. The chest is an ancient language - there is a book on this already in the game that deals with the language of Faery.
2. You need to split you characters - one for each route.
1. Check the library in Cyseal (first town). For sale
2. You need to move to hit all teh plates without being detected - any of the statues turn red backtrack and start again when they turn green. Sneak helps.