Question about the Dawnchant

[J. Magi she/her]

Please bear in mind it's been a few months since I read these books, and it's possible I've just forgotten something important--this question has been floating around my head for a while. 

Anyway, at the end of Oathbringer it's revealed that the Dawnsigners are actually Listeners/Parshendi right? And we know this because scholars were able to translate some old texts using the stuff Dalinar said in his visions as a guide. 

But this implies the Dawnchant is one language. If the Dawnsingers were writing about the humans coming to Roshar, they would obviously speak in their own language--probably something similar to the "ancient" that Leshwi and the other fused use. But then, can what Dalinar uses in the visions be the Dawnchant? Surely the humans had their own language at the time (maybe several languages) so it seems unlikely that everyone would speak the same language. Especially with the fact that the Dawnsingers used the rhythms, and the human people obviously could not. The humans would probably speak some version of what they used to speak before they came to Roshar. 

I realize its possible that they are speaking the same language, and the humans are just not using the rhythms (the way Rlain can speak in Alethi y'know?). But it seems unlikely that the language the Dawnsigners spoke before humans came to Roshar is the same language that humans spoke several thousands of years later during Dalinars visions. But somehow, scholars and ardents are able to translate one using the other as a key. 

So how can the Dawnchant be one langauge? Is it more than one? 

I hope this isn't too confusing, and I realize it's probably deep diving into speculation, but I'm curious if anyone can explain this or provide more info.

(also pls keep in mind I haven't read RoW yet, if the answer is in there, just let me know and I'll find it as I read ^^)

[Quantus he/him]

The Dawnchant is the language of the ancient Singers and is "the root of the Dawnate language family, consisting of the Shin, Parshendi, and Horneater languages. While the vocabulary of these languages varies greatly, they share similar grammar.^[2]"  I think the language of the immigrants just became the basis for some/most of the other languages still floating around (potential world-hopping alien influences notwithstanding).  But Language overall wouldnt have been an insurmountable barrier for them, they'd have been using a lot of Connection shenanigans to understand each other.  The Immigration and the first War and Fused and whatnot all happened within a single generation, so culturally things were moving very quickly.