Apparently Turkish DGCA has produced a statement that they will only issue validations for ICAO licenses if 2 examinations are undertaken in Ankara.
I heard from a friend that these examinations are very difficult and to an ATPL level.
For this reason Pegasus informed me that they will not interfere if you have an ICAO license and said that I am welcome to sit the exams myself prior to applying. For this reason I decided not to.
If you don't have a JAR-FCL license then I recommend you don't apply. Just a Turkish license or JAR license is acceptable to them.