The original languages on the continent of Trema were various local dialects of Jenelesti (the Elvish language that the native Elves spoke; Elves controlled most civilized territory), Herethim (spoken by most of the humans who lived in the eastern and central areas, primarily roaming tribes), Gresian (spoken by the slightly more civilized human cultures in the western lands, and Kelaquois, spoken by the real savage humans in the northlands.
There were also the Jispin, who had an advanced caravan culture, but their language was particularly prone to shifting as they changed from area to area; the core of the language remains the same, but much of it blends with whatever area they're in. In the southern half of Trema (the continent's kinda split in two, like America), the Chaopin language was spoken by some of the first humans, and one of the few human civilizations. This language got picked up by numerous goblinoid races that may have been created through Chaopin magic.
Dragons had their own language, as did the fey, but those languages were somehow ingrained in their existence, and do not change.
Around 4000 years ago, the Serens arrived from over the sea, landing in eastern Trema and conquering widely. By about 3000 years ago, they controlled most of the continent, and had driven most other cultures into isolated pockets. The Seren language mingled with the local languages, and in some places languages just drifted, so that by 3000 years ago you have Seren, Gresian, Herethim, Kelaquois, traditional Jenelesti, the split languages of Shahalesti, Taranesti, and Kohalesti, Chaopin, Jispin, Leylandish, Cavalesh, and Ragesian.
The Ragesian Empire conquers the entire world, and then falls about 200 years later, creating an age of darkness that took thousands of years to climb out of. In the time that passed, Shahalesti split into Innenlesti, Vaneljesti, and Tundanesti; Chaopin died out but Geidon and Aechani developed; Cavalesh derived into Lyceian; Ragesian spawned Sindairese and Dorisian; Seren died out then came back as Tennae; and Herethim mingled with a few other languages to create Nau-Herethim. No one really speaks Seren, Gresian, Herethi, Jenelesti, Chaopin, Leylandish, or Ragesian anymore, but they're noteworthy for study.
Toss in Draconic, Fey, various celestial and infernal languages, the elemental dialects, and all manner of unknown languages in the land below, and I think I've got a pretty diverse set of languages. I hope I didn't forget any.