Kurmanji, major Kurdish tongue

There are two main branches of the Kurdish language. The Kurmanji group, which consists of northern Kurmanji spoken mainly in northern Kurdistan is the dominant language. There is also Sorani, spoken in the south..  Pahlawâni or Pahlawânik is another branch and that has two main dialects, Dimli or Zaza and Gurâni,

Eli Bedir Xan aka Ali Bedir Xan  1893-1951
Obviously that is part of the problem here, there is no unifying language for the Kurds to unite under.  Worse, neither s there a written syllabus for communication as it was not until  1943, that Jeladet  Elî Bedir-Xan, a Kurdish diplomat serving in Istanbul,  published the journal Hawar,  transcribing  Kurmanji using Roman script instead of either Arabic or Persian calligraphy.  
His reason was that getting a hold of Roman presses was far easier, but it also added to the subterfuge as neither Arabs, Persians (later day Iranians) could easily read it.  His grammar can be found over here in downloadable pdf form from Professor W. M. Thackston of  Harvard University, if you are interested in seeing and/or learning it.
Hawar was circulated clandestinely within Turkey & contributed greatly  to the rising  Kurdish literacy.  It was a great though secret success though it is still far from being a normalised grammar, though many Kurdish emigres are helping there in their new homes.  Also, if you search for Kurdish you will see a lot of Cyrillic lettering, that is because of the Soviet occupation from the 1950’s on and so also you will find a lot of Russian words coming into the language.  The one I spotted the most was “MIR” (World or Peace).
Still there are about 3000 words in the Kurdish dictionary using a modernised Turkish Latin alphabet and there is a Kurdish-English Dictionary by Michael L. Chyet published by Yale University Press in 2003 that is available.  There is also a much larger vocabulary by Barn Rizgar with about 25,000 Kurdish words and phrases that was published earlier by M. F. Onen, London, in 1993 as well as an online dictionary at Ferheng.org.   It also has a Sorani and Zazki component.
Why Bedir-Xan chose Kurmanji instead of Sorani was also a simple affair:  Sorani was and is still considered the literary language of the Kurds.  It was not until after the fall of the Turkish Empire in WWI,  that  Colonel Tawfi  Wahbi transcribed it phonetically; but still it has not caught on.  Nor could I find any reference outside of the book on him and his endeavour.  
Probably though Bedir-Xan being a native Kurmanji speaker favoured his own native tongue as well.  He definitely would have been far more familiar with it, as Sorani’s like Kurmanji is part of the larger Indo-Iranian branch of  Indo-European family. 
While closely related to Kurmanji,  Bedir-Xan  considered Sorani to be an “offshoot” of the former, but the two languages are neither mutually intelligible nor structurally (syntactically) similar to each other.  It would be like a Romanian speaking French, he may get the general idea when it’s written, but spoken the Romanian would be at a loss despite the two being Romance languages.
Finally when considering the odds, they are also in Kurmanji’s favour.   It has  18 million speakers while Sorani has 6 million  .  This latter point figured prominently in Bedir-Xan’s decision,  as he noted in the first issue of Hawar in French btw, the universal language of diplomacy & literature at the time particularly in the Middle East.
Biblically or archaeologically, there is no record of Kurdish writing, which would not be astounding considering their nomadic lifestyle.