When the Snake-Men created the 13 races of mankind, they imprinted within each the ability to spontaneously, organically develop a unique racial language. Why did they care if their lab rats could speak? No one knows.
There are 12 ‘mother tongues’ among Men, one for each color, excepting Dolm. There are several additional languages that have developed over the eons. Language notes in brief:
- There are no alignment languages on CARCOSA.
- Dolm Men do not have their own language; during childhood, they randomly imprint one of the 12 color languages. The reason for this is unknown.
- Black Tongue is the primary language of Black Men and – due to abundant overlap with other languages – the unofficial lingua franca of CARCOSA.
- Dark Black is a baroque dialect spoken only among a small, xenophobic polity of Black Men who desire utter distinction from all other races.
- Grave Cant aka Bone Speak relies upon important visual cues only reproducible by Bone Men: subtle sparking displays among nervous tissues, prominent organ discoloration, and altered circulatory rhythms. It is essentially unlearnable by other races. Dolm Men who imprint Bone Speak typically devolve into animalistic savagery.
- High Green and Low Green are two distinct languages, the former native to civilized Green Men and the latter a debasement in use solely among Green Primitives.
- Blue and Red are near enough to be largely interchangeable. This linguistic familiarity explains the close cooperation between these two races.
- Orange is sung among family and friends, spoken to anyone outside the tribe.
- Purple is a barbaric cacophony of hoots, whistles, and screeches barely more advanced than the calling of apes.
- Ulfiric is modulated to affect the emotional centers of the mind. Uniquely skilled speakers can evoke spectacular responses in weak-willed listeners: hypnosis, suggestion, charm, and more.
The Doomed World CARCOSA 
You’re an asshole but I’ll admit you’ve got a handle on Carcosa.
Haha, only my family & friends are supposed to know I’m an asshole!
Interesting post. I myself just stick with Common, as adding language difficulties just drives players nuts, in my experience.
Black Tongue can take the place of Common. If you want to keep it simple, PCs get their color language and Black Tongue to start and everyone they encounter gets Black Tongue as well.