The Sogdian language belongs to the eastern group of the middle iranian languages, along with Sacian, or Saka (spoken in Khotan, China), Bactrian (spoken in present-day Afghanistan) and Chorasmian (spoken in present-day Northern Uzbekistan). It was originally spoken in Sogdiana, a historical region situated around Samarkand. Other languages of this group are Avestan in the old times and Pashto and Ossetian in the modern times. In the first millennium A.D. it has served as a lingua franca of Central Asia, and it was used both as a means of oral communication and for written purposes, in fact since the beginning of the XX century many excavations have brought to light numberless documents composed in this language, that testify its outmost importance and diffusion in that area. It was a literary language for Buddhism in Central Asia, but also for Nestorian Christianism and Manichaeism.
This language has not died out after its decadence, but it has evolved into the Yaghnobi language, spoken in Tajikistan by a few thousand people, and it has been replaced as a cultural language by Persian, a western iranian language.
Links
The best site about Iranian languages: iranianlanguages.com
Learn Sogdian at Harvard on line! www.fas.harvard.edu/~iranian/Sogdian/index.html
Sogdian dictionary: www.uni-koeln.de/phil-fak/indologie/lil/sd-search.html
Sogdian tales, PDF format: www.azargoshnasp.net/~iran/languages/Sogh/soghdiantales.pdf
An interesting article about Sogdiana from the online magazine The Iranian: www.iranian.com/History/2001/July/Sogdiana
Christian manuscripts in Sogdian found in Turfan, Xinjiang: www.bbaw.de/forschung/turfanforschung/dta/n/dta_n_index.html
Sogdian-L, a forum for the discussion of the history of Sogdian communities: groups.yahoo.com/group/Sogdian-L