—Reyson speaking the Ancient Language (translated) and Naesala speaking the Tellius Language, the first time the player is informed of the difference
The Tellius Language is the main language used on the continent of Tellius in the Tellius Series, as opposed to the Ancient Language of old, which was forgotten over time. The Tellius Language is spoken almost exclusively by Beorc, although some Beorc magic users know the Ancient Language for the purpose of spell incantations. In addition, some Laguz have also learned it through contact with Beorc. The term is first used by Nailah when Volug, Rafiel and herself travel from Hatari, where the Ancient Language is still primarily used.
Like with the common language in other Fire Emblem games, the Tellius language is represented as the player's language. Ike speaking the same language in crossover appearances such as Fire Emblem Fates and Fire Emblem Heroes suggests that the Tellius language is identical to other common languages in the Fire Emblem multiverse.