Iranian languages
New Iranian

Following the Arab conquest of Persia, there were important changes in the role of the different dialects within the Persian Empire. The old prestige form of Middle Iranian, also known as Pahlavi, was replaced by a new standard dialect called Dari as the official language of the court. The name Dari comes from the word darbâr (دربار), which refers to the royal court, where many of the poets, protagonists and patrons of the literature flourished. The Saffarid dynasty in particular was the first in a line of many dynasties to officially adopt the new language in 875 CE. Dari may have been heavily influenced by regional dialects of eastern Iran, whereas the earlier Pahlavi standard was based more on western dialects. This new prestige dialect became the basis of Standard New Persian. Medieval Iranian scholars such as Abdullah ibn al-Muqaffa (8th century) and Ibn al-Nadim (10th century) associated the term "Dari" with the eastern province of Khorasan, while they used the term "Pahlavi" to describe the dialects of the northwestern areas between Isfahan and Azerbaijan, and "Pârsi" ("Persian" proper) to describe the dialects of Fars (Persia). They also noted that the unofficial language of the royalty itself was yet another dialect, "Khuzi", associated with the western province of Khuzestan.

The Islamic conquest also brought with it the adoption of the Arabic script for writing Persian and much later, Kurdish, Pashto and Balochi. All three were adapted to the writing by the addition of a few letters. This development probably occurred sometime during the second half of the 8th century, when the old middle Persian script began dwindling in usage. The Arabic script remains in use in contemporary modern Persian. Tajik script, used to write the Tajik language, was first Latinised in the 1920s under the then-Soviet nationality policy. The script was however subsequently Cyrillicized in the 1930s by the Soviet government.

The geographical regions in which Iranian languages were spoken were pushed back in several areas by newly neighbouring languages. Arabic spread into some parts of Western Iran (Khuzestan), and Turkic languages spread through much of Central Asia, displacing various Iranian languages such as Sogdian and Bactrian in parts of what is today Turkmenistan, Uzbekistan and Tajikistan. In Eastern Europe, mostly comprising the territory of modern-day Ukraine, southern European Russia, and parts of the Balkans, the core region of the native Scythians, Sarmatians, and Alans had been decisively taken over as a result of absorption and assimilation (e.g. Slavicisation) by the various Proto-Slavic population of the region, by the 6th century CE. This resulted in the displacement and extinction of the once predominant Scythian languages of the region. Sogdian 's close relative Yaghnobi barely survives in a small area of the Zarafshan valley east of Samarkand, and Saka as Ossetic in the Caucasus, which is the sole remnant of the once predominant Scythian languages in Eastern Europe proper and large parts of the North Caucasus. Various small Iranian languages in the Pamir Mountains survive that are derived from Eastern Iranian.
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