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Everyone speaks Common/modern Aveyronnais.

Extra language slots could be spent on this non-exhaustive list:

  • Cozovodë, the language of the Elven empire to the east
  • Gravonian, the language of the pre-human period, known only to a few scholars
  • Rat, the language still spoken by many Rat people among themselves (related to Gravonian, or descended from it, with certain phrases being mutually intelligible)
  • Archaic Aveyronnais, spoken/written from the founding of the Empire to about the 8th century; you would need this to read the Almas Genara in the original, for instance
  • Middle Aveyronnais, spoken/written from the 8th century to the 15th or so; intelligible with Modern Aveyronnais in about the same way Chaucer is with modern English (i.e. somewhat, but it takes practice to get the hang of reading it)
  • Psyrene, spoken in the extreme south-east of the Empire and also some old texts (the most recent large territory to be brought into the Empire, about 400 years ago, still culturally distinct in some respects)
  • Plascencial, formerly spoken in the south of the Empire but now basically extinct except in old texts
  • Shadar-kai, the language of the inhabitants of the Shadow Plane
  • Draconic, the language of magic, and of long-dead giant flying creatures
  • Austvagoy, the language of the far northern elven nomads

Other options may be available - speak to the GM!