Kurdish is a continuum of Northwestern Iranian languages spoken by the Kurds in Western Asia. Kurdish forms three dialect groups known as Northern Kurdish (Kurmanji), Central Kurdish (Sorani), and Southern Kurdish (Palewani). A separate group of non-Kurdish Northwestern Iranian languages, the Zaza–Gorani languages, are also spoken by several million Kurds. Studies as of 2009 estimate between 8 and 20 million native Kurdish speakers in Turkey. The majority of the Kurds speak Northern Kurdish ("Kurmanji"). 

The literary output in Kurdish was mostly confined to poetry until the early 20th century, when more general literature began to be developed. Today, there are two principal written Kurdish dialects, namely Northern Kurdish in the northern parts of the geographical region of Kurdistan and Central Kurdish further east and south. Central Kurdish is, along with Arabic, one of the two official languages of Iraq and is in political documents simply referred to as "Kurdish". 

The Kurdish languages belong to the Iranian branch of the Indo-European family. They are generally classified as Northwestern Iranian languages, or by some scholars as intermediate between Northwestern and Southwestern Iranian. Martin van Bruinessen notes that "Kurdish has a strong south-western Iranian element", whereas "Zaza and Gurani [...] do belong to the north-west Iranian group".
Which one?
Iraq