Some languages that are common in Faerun in general are not very useful in Chult, and players should be aware to not waste a slot on a language that will likely almost never be used in a long campaign. *Not having these languages wouldn't impact * the campaign very much:
On the other hand, as a land filled with primordial spirits and cryptic species, certain languages that are exotic elsewhere would be relatively more frequent in Chult:
- Chultan: a second "common" language. Even creatures that speak human languages are more likely to speak Chultan than Common. Uses the Draconic alphabet.
- Elemental languages: Aquan, Auran, Ignan, Terran
- Planar: Celestial, Abyssal, Infernal
This list is in no particular order, except Chultan, which is widespread. The other languages will occur here and there, just with a higher frequency than in the Sword Coast for example.
As for any other human or racial languages (such as Dwarvish and Gnomish), the frequency should be on average about the same as elsewhere in Faêrun.
For the Archeologist or Anthropologist backgrounds only, a dead language is available: Old Omuan. Much like ancient Egyptian, nobody remembers how this language was spoken, as only the written form survives.
Finally, a curiosity about the Common tongue: the one spoken in Chult is a dialect called Kouroo. Doesn't hinder communication but it's different enough that people coming from afar will keep sounding foreign for years until they master all the differences.