Elven - Aeonesti - Ceralnesti, Elenesti, Jhaerenesti

The first language spoken by higher lifeforms on Creacia beginning at the Dawning, Aeonesti is considered to be the mother of all goodly, terrestrial languages and the heir to Celestial. It is the direct ancestor of all Elven languages and is integral to the origins--if not the modern forms--of Arenundim (Dwarven) and all various Feyfolk, Beastien, and Human languages. The High Elven linguist Beriliam Sha'nav famously wrote, "Without Aeonesti, there is no language except grunts and growls."
Aeonesti is the only form taught to non-Elves, while the various languages of the Keth'talisen--Ceralnesti (Wood Elven), Elenesti (High Elven), Jhaerenesti (Wild Elven), and Drow--are kept secret amongst each of the Five Families. (The Seirenesti, or Sea Elves, have no spoken language beyond Aeonesti, but rather communicate telepathically). The punishment for teaching an outsider one of the family languages can range from public castigation, to exile, to execution.
When spoken by Elves, the language is considered one of the most beautiful and flowing in existence, with soft consonants and lilting syllables, almost song-like (although most Elves claim that it is butchered by anyone but Elves, of course). The written form is in the Aeoketh Script, similarly the oldest known terrestrial alphabet (outside of the Six Eternal Languages. The actual writing of it (or carving it) proved so difficult for non-Elves, however, that it is rarely used outside the Keth'talisen.