Let's face it. 99.9% of expats spend their money overseas, whether short term or long term, whether it's US Dollars, Euros, Pounds, Aussie Dollars etc. So this 20% pay rise is just complete BS. It's purely a rapidly declining currency, and 20% in real terms is actually a pay DROP in your home curency!
Get used to seeing these campaigns from THY, as they will be one of the very few Airlines that can spout these supposedly "substantial" pay rises, all the while their costs are reducing. When you buy a THY ticket in Turkey, whilst it is charged in Lira, the price increases according to the exchange rate of a real currency. Therefore with strong solid income for them and reducing salaries for you (THY employees), THY is doing just fine
There are good points to the long haul gig, but the pay rise is a BS gimmick campaign. Go in informed and with your eyes wide open.