During the course of the game, you'll find documents written using the Raanaar alphabet. At the start of the game you won't be able to read them, but if you can find the three books describing the language, then you'll be able to read the documents.

Here is where you can find the three books.

Part 1: Basic Studies (Act One, Prison Level 2, statue room)
Part 2: Intermediate Studies (Act Two, Shaman's Realm)
Part 3: Advanced Studies (Act Three, Temple Catacombs, Level 6)