In COMICS Raven is a half-demon and half-human possessing many abilities inherited from her father Trigon. She grew up in an alternate dimension called Azarath, with pacifistic inhabitants whose spiritual leader was the mystic Azar.
Azar planned to expel all evil from the Azarathians so that the demon Trigon could use the dark energy to be resurrected and then Azar could finally kill him (NOTE: This ill-conceived plan is similar to that of Lyon Vastia's when he used the Moon Drop to release the demon Deliora from the Iced Shell Ur cast upon him in Fairy Tail).
The manta (or chant) Raven uses in the Teen Titans cartoon ["Azarath, Metrion, Zinthos!"] is similar to her mantra and spell-casting she uses/used in comics pre-New 52. Primarily she uses her manta to ease her meditation and as a focus point. As she learned her meditation in Azarath it is my understanding that it is a magical language or words of magical power she draws strength from.
If the words are a specific language it is probable it is Azarathian?
According to the DC Comics Wiki:
Raven is fluent in several languages including English, German, Latin, Romanian, Ancient Sumerian, and Sanskrit.
Raven is well-versed in the occult and is familiar with the magical and mystical rites from both her home dimension Azarath as well as Earth.