Pahlavi as a linguistic entity

One of the earliest preserved accounts of the linguistic condition in ancient Media in Arabic sources is found in Ibn al Nadim's 10th century work, which quotes an older author, Ibn al Muqaffa (8th century):

'Abd Allah ibn al-Muqaffa' said, "The languages of the Persians are the Pahlawi, the Deri, the Parsi, the Khuzistānī, and the Syriac, The Pahlawi (al-Fahlawiyah) is related to Pahlav (Fahlah), a region which includes five cities: Işbahan, Rayy, Hamadhan, Mah Nahawand, and Adharbayjan. The Deri (al-Durīyah) was the language of the cities of al-Mada'in, spoken at the king's court. It was derived from presence at the court (al-bab), coming chiefly from the language of the people of Khurasan and the East, the speecli of the people of Balkh. Priests, scholars, and their like speak Parsī (al-Farsiyah), the speech of the people of Fars. The kings and nobles used to speak the Khuzistānī (al-Khūzīyah) in privacy, in places of play and amusement, and with their retinues. The people of al-Sawad used to speak Syriac (al-Suriyānīyah), writing in one form of Persian Syriac.

Ibn al Muqaffa's testimony is enigmatic. Much has been said about what the various designations may indicate for Ibn al Muqaffa. The better question is to determine what the plausible scenario on the ground was and how it related to Ibn al Muqaffa's description. A popular but incorrect assumption from the text is that 'pahlavi' was a standardized and uniform dialect or language. This cannot have been the linguistic condition in the eighth century, nor was there a single dialect/language in that region for centuries afterward. The 'pahlavi' label, as a linguistic entity, would be an amalgamation of multiple languages over centuries, many of which would be mutually incomprehensible to speakers of two different languages/dialects in the region. The plot becomes more interesting, but also more difficult, as the ethnic label of the Kurd-label in Arabic sources during the early centuries is considered. Kurdish, as a linguistic entity, was unknown for most of the premodern period and not named as such. The Kurdish language(s) would be placed under other generic labels, Pahlavi being one example. 

Albanians and Kurds defeating Napoleon's army

In an epic poem preserved in a manuscript dated to 1806, the Albanian and Kurdish troops who defeated Napoleon's army during the Siege of Acre (1799) are praised for their defense of the local population:

"Where are the people of Acre, a wall protecting the women?

O sekmen, hurry! I do not want to hear excuses!"

They pounced upon them like countless lions,

The Arnā'ūt and Kurds, their breasts boiling with zeal.

They drew their swords like lions,

Seeking the reward of palaces and hūrīs in Paradise.

They made religion (al-dīn) triumph, their faces pale,

Selling their souls in exchange for reward in the next world.

Ayyubid headcap and contemporary Kurdish headcap

Do contemporary Kurdish caps (klaw) and the headdress used by the Ayyubids have any similarities? Yes, indeed. The Mamluk historian Al-Qalqashandi makes reference to the Ayyubids' headdress.

Al Qalqashandi (15th-century):

Their costumes differ depending on which part of the body they cover. As for the headgear, it was explained earlier that the Ayyubids used to wear yellow caps (kalawtāt) without turbans and that they hadhair locks (dhawā'ib sha'r) that they loosened behind their backs. In his reign, al-Ashraf Khalīl b. Qalāwūn changed the colour of the caps to red instead of yellow, and ordered wearing turbans upon them. This remained the case until al-Malik al-Nāşir Muhammad b. Qalāwūn went on pilgrimage towards the end of his reign and shaved his head, so everyone shaved theirs, and they continue to do so until now. Their turbans used to be small, until they were enlarged in the reign of al-Ashraf Sha bān b. Husayn, which resulted in a more beautiful and finer shape [of turbans] that remains [the case] up to our times.