Based on different measures, following Kurdish dialects dominate Kurdistan:
Population: Kurmanji
Distribution: Kurmanji
Medieval literature: Kurmanji + Hewrami (Gorani)
Easier to be understood by speakers of other dialects: Kurmanji (It simply has lost musch of gramatical features)
Modern literature: Sorani
Current Offical status: Sorani
Being understood by most of Kurds in south and east : Sorani
So you see that it is difficult to choose which one has a higher hand among the Kurds.
But Diri Sorani (central Kurdish) is gramatically very very close to the dialects spoken in southeastern Kurdistan known as southern Kurdish or feyli, kirmanshani, xanaqini, kalhori, ilami etc. the main difference between sorani and these dialects is that they use a higher number of farsi loanwords than Sorani does. and I think that they and Sorani-speakers can very easily communicate. In my opinion southern Kurdish to central Kurdish is similar to Badini to Kurmanji used in north.
One thing more is that Gorani (hewrami) which is a very archaic form of Kurdish is only spoken in a very small enclave located between Sorani-speaking area and southern Kurdish speaking area (north of kirmanshah and south of Slemani). I estimate them to be lesser than one mllion since most of them in recent century have shifted to Sorani and the remaining are mostly able to speak Sorani. My aim is to show you that Sorani is naturally dominant in eastern and southern Kurdistan, and is rapidly 'devoloping' as a 'modern' language with a lot of technical and non-literature terms and expressions.
To conclude I'm trying to say: While all dialects and languages of Kurdistan Kurmanji, Sorani, Hewrami (Gorani), Zazaki and even kelhori, Leki, Ilami (+ Aramaic, Arabic Armenian etc..) should be an official language of their respective regions, but we have to agree that based on many factors Sorani and Kurmanji dominate Kurdistan, AND it is difficult to choose between these two too. A semi-natural and scientific modifying of one of these two dialects (sorani and Kurmanji) by the other one, preferebly a Kurmanjizied Sorani (for many reasons mentioned above in my previous post plus the fact that Sorani enjoys a better official opportinuty than Kurmanji does) smoothes the path towards assimilating of current standard Kurmanji and current standard Sorani into one well-miexd and popular standard Kurdish dialect in less than one decade.
I hope clarified my spot enough.











