Why do some races not have racial languages?

Devora

Why do some races not have racial languages? If I'm not mistaken, the list is: human, illithoid, kephera, trill, viscanti. The illithoid are psychic, that makes sense. 

Humans are from another world, aliens really, but why wouldn't they have brought along their own language?

I also don't get why kephera, who were secluded in the Undervault for so long, would have learned Common but never come up with their own language. Unless they use pheromones or something?

No idea what happened with trill. Is it because of music being their true language? @Shaddus You've mentioned discussing this with Isune. Can you share that lore or would you prefer people discover it in-game?

Viscanti probably makes sense. Still wondering why they haven't made their own language in the aeons *since* they became transformed by the Taint. 

I have the same question about faeling, who still share the elfen racial language even though it's been awhile. Why wasn't the fae language mixed in to make a unique faeling language?

Any lore tidbits about this are welcomed! Obviously some of the reasons may be OOC, but I'm mainly looking for IC explanations. You can also rp an answer with me, thanks!

Maligorn

Both kephera and illithoid communicate psionically.

Luce

Most of the time languages aren't something developed because the group is unique, but because the group is isolated. Trill most likely developed with Lucidians, and if they had access to any racial language it probably would have been theirs. Likewise Viscanti and Faeling already had thriving languages spoken around them by the time they developed as truebreeding races. 
As for humans, their racial language is common.

Arix

If the human racial language is common, what language did the Holy Celestine Empire use as common before that?

Devora

I second @Arix's question. Would be interesting if everyone had been required to learn merian. Or maybe there was already a Common before humans came, but then the language of humans just mixed in with that Common?