The following are some of the languages spoken in the world of Greyhawk. They can be learned with the Speak Language skill, though exceptions may apply where noted. Unless your character speaks a particular language, assume that knowledge or recognition of it is OOC information.
Gnome: the racial language of gnomes, it is written with the runic Dwarven script, though often in a more whimsical style. It is renowned for its technical and legal treatises, and catalogues of knowledge about the natural world. Many human herbalists, naturalists, barristers, and engineers learn Gnome in order to read the best books about their field of study.
Goblin: the racial language of goblinoids, including goblins, hobgoblins, and bugbears. It is written using the runic Dwarven script, though often in a cruder style--when it is written at all, for few such creatures have the patience or interest to learn their letters. It frequently uses harsh, guttural sounds, especially “r,” “g,” and “k.”
Gol-Kaa: the racial language of goliaths, a race of massive, stony-skinned nomads. For millennia, goliaths only had a spoken tongue, Gol-Kaa, which has only thirteen phonetic elements: a, e, g, i, k, l, m, n, o, p, u, th, and v. Around the tenth century CY, goliaths picked up the runic alphabet of the Dwarven language, though the concept of a written language still hasn't spread to all the tribes yet. Those tribes that have learned the Dwarven alphabet have transcribed much of their vast oral tradition into carvings, cave paintings, and even books. Goliaths are rarely seen outside their tribes, though resources on their language can be found in larger cities.
Grell: the racial language of grells, fearsome carnivores that look like giant brains with a vicious beak and 10 dangling tentacles, each 6 feet long. Grell have a weird language composed of bird-like squawks and chirps, combined with tentacular motion and a limited telepathy with other grell. Other creatures cannot learn the grell language, and they would not deign to learn the language of "lesser beings" (a synonym for "food" in their language).