There are many languages in the world, but everywhere along the full length and breadth of the known territories, the need for trade has prompted an almost informal new language, simply referred to as the Common speech. It borrows from the languages of specific peoples in an almost haphazard fashion, featuring dwarvish words for engineering, elvish artistic nuances, and a convoluted grammatical structure cobbled together primarily from the speech of the Dasseni and Chathian peoples. In addition to this language, characters should choose languages from the following list.

Kelaquan, language of Kelaquois, the ethnicity of humans in northern Ragesia.
Latian, language of Latia, the ethnicity of humans in  western Ragesia.
Chathan, language of Chathus, the ethnicity of humans in southern Ragesia.
Morrun, language of Morrus, the ethnicity of humans in central Ragesia.
Dasseni, language of the Kingdom of Dassen. (The people of Gate Pass primarily speak this language.)
Sindaireese, language of the Exarchate of Sindaire.
Ostalan, language of the Khaganhold of Ostalin.

Elvish, language of the Shahalesti elves, amongst others. The Elves are noted in linguistic circles for the care taken not to allow their language to diverge (or devolve, as they might put it themselves). This even extends to their offshoot races, such as the elves who live under the sea or the nigh mythical subterranean dark elves.

Dwarvish, language of the Dwarven Clans whose primary home is Dassen. Dasseni in fact shares the grammatical structure of Dwarvish, though none of its vocabulary. Family clan variances are common enough to create the occasional minor misunderstanding, but it's rarely problematic.

Orcish, language of the Orc Tribes, shows a great deal of variance. However, the majority of tribes have since adopted the speech of Empreror Drakus Coaltongues people, and it is to this dialect that people now refer when they speak of Orcish.

Celestial, language of angels and the like, arose in Heaven untold ages ago as the gods themselves first formed words and began to name things. This language has a bewilderingly precise vocabulary, but a simple grammatical structure. Some scholars claim all other languages have their roots in Celestial, tracing many words back to original celestial forms.

Infernal uses Celestials vocabulary word for word, allowing the diabolic creatures that now rule that world to communicate with the celestial peoples readily enough. However, Infernal possesses a downright sadistic grammatical ruleset, making it quite easy to layer multiple meanings into the same basic sentence. You must first know Celestial before you may learn Infernal properly.

Abyssal is something of an anomaly. The many beings that reside in the Demon World show little in the way or rhyme or reason to their existence, and continuously wage genocidal conflict amongst themselves. And yet, their headache inducing complicated and inconsistent speech is universal amongst them.