Eastern Iranian languages

The second-largest living Eastern Iranian language is Ossetic, with roughly 600,000 speakers across Ossetia (split between Georgia and Russia).

[1] Western Iranian is thought to have separated from Proto-Iranian in the course of the later 2nd millennium BC not long after Avestan, possibly occurring in the Yaz culture.

[2] Middle Persian/Dari spread around the Oxus River region, Afghanistan, and Khorasan after the Arab conquests and during Islamic-Arab rule.

Only a few speakers of the Sogdian descended Yaghnobi remain among the largely Persian-speaking Tajik population of Central Asia.

This appears to be due to the large numbers of Persian-speakers in Arab-Islamic armies that invaded Central Asia and later Muslim governments in the region such as the Samanids.

The neighboring Indo-Aryan languages have exerted a pervasive external influence on the closest neighbouring Eastern Iranian, as it is evident in the development in the retroflex consonants (in Pashto, Wakhi, Sanglechi, Khotanese, etc.)

[8] A more localized sound change is the backing of the former retroflex fricative ṣ̌ [ʂ], to x̌ [x] or to x [χ], found in the Shughni–Yazgulyam branch and certain dialects of Pashto.