But the money the company pays to the government is much higher on behalf of the local (~35%), than for the expat (~5%)
Most of the salary for the locals is technically a flight compensation, pretty much tax-free hence a small difference in costs. Insuring, getting a working permit for, training and paperwork handling for a expat pilot is more costly.
Reclaiming your pension fund is a pretty easy thing to pull off. If you've worked for a couple of years in Turkey, you might be able to reclaim quite a nice little sum of money.
And for the people crying for an upgrade on a flag carrier as if it was something they were entitled to automatically after only a few years in the company, I'm speechless. The market is relatively good at the moment for experienced pilots and will by the looks of it turn down soon. Vote with your feet or be a man and suck it up.
It's business after all and not about babypowdering bums just because you have a license. Remember that a teacher, engineer, doctor, technician, crew planner etc in Turkey typically makes less than 15-20% of what a first officer at THY makes. The business ticket is something that the union managed to get through against the will of the management.