Part 1 - Djinnistani

From the Daevapedia Wiki: The language of the Daeva tribe. Described by Nahri as sounding similar to Hebrew, though Yaqub adamantly disagreed (City of Brass, Ch.1, p.17). When discussing with fans about writing some Divasti dialogue, the author wrote, "there was an embarrassing amount of time spent with proto-indo-european roots" (Chakraborty, Twitter, 4/13/2020) (1).

First of all, what is Proto-Into-European? It’s the “reconstructed common ancestor of the Indo-European language family”, which contains about 446 living languages spoken by over 3.4 billion people (2). That’s quite a lot, but we can narrow it down geographically.

This is a map of West Asia slapped on top of the Daevabad map from City of Brass. I made this overlay a while ago (in Google Slides, please excuse the quality), and while it’s not a perfect match, it gives us a better idea of which countries (and languages) make up Daevastana. In case the map text is too blurry, this region includes Iran, Turkmenistan, Uzbekistan, Afghanistan, Tajikistan, Kyrgyztan, and Pakistan.

This region overlaps with the Iranian (or Iranic) branch of the Indo-European Language Family, shown by this map (3): 

So here's my question: The Daeva tribe adopted the original name of their species as their tribal name. Did they do the same for their language? IE, is Divasti the original language spoken by the Daevas pre-Suleiman’s curse? In that case I want to look for the oldest language spoken in the “Daevastana” region.

The Iranian language family is chronologically classified into Old, Middle, and New Iranian, with evidence of only TWO Old Iranian languages surviving. These are Avestan, and Old Persian (4). Avestan was originally spoken from around 1500 - 400 BCE (8), and Old Persian was adapted to cuneiform around 600 - 500 BCE (6).

Fun fact, Old Persian would have been the language used around the time of Darius the Great, whose name is a derivation of... Darayavahoush (9).

Avestan was already a dead language known only to priests by the 5th century AD, so I doubt any modern production would be able to adapt it for use as Divasti (5). That leaves Old Persian, which is a DIRECT ancestor of New Persian, aka, Farsi (6). Farsi is the most commonly spoken language of the Iranian language group (4). It has been spoken in its current stage since around the 8th century, and has around 127 million speakers today, predominantly in Iran, Afghanistan, and Tajikistan; all of which are located in "Daevastana" (7).

Here's a map of Farsi-speaking areas overlaid with the Daevabad map from City of Brass (10).

TL;DR: Divasti - Farsi/Persian

Bonus info and works cited under the split :)