For the most part, those books to learn languages helps you learn the basics of the core races of Norrath (barbarian, dwarf, gnome, halfling, etc....). However, there seems to be some quests for NPC races like Gnolls that you can learn more about them and understand them in battle.
Hopefully this ends up working out very well where an Illusionist could learn the Gnoll language, cast Gnoll illusion, and go into Blackburow and be able to chat with some of the gnolls to start quests for them :P