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!