We have difficulty in developing games because there is no Turkish interface
(google translate)
While I dont want to say your request is bad, I honestly doubt that UE supporting turkish will help you in development. Almost all informatic/programming sources, softwares and documentations are in english. The same applies for issues and help/answers that you can find on the internet. Even if UE supports turkish, you still wouldnt be able to develop smoothly if you cant speak english because most of your resources/softwares and most of the stuff in the internet does not support turkish.
Take this as a friendly advice: You and your team is better off learning english rather than relying on turkish support
Edit:
I seriously mean it: your team is going to waste a lot of potential if you dont learn english.