Türkçe Dil Desteği GOG Galaxy'e ne zaman gelecek?
When will Turkish Language Support come to GOG Galaxy?

Katılıyorum. Uzun süredir severek kullandığım bir uygulama lütfen artık Türkçe dil desteği gelsin !!!!
I agree. An application that I have been using for a long time, please get Turkish language support!!!!

Relevant community wishlist entry:
Turkish language should be applied.

Hello from a distant place in the world! Just voted to support your request.

My hovercraft is full of eels.

The better question is; When will Turkish Lira support will come to GOG Galaxy? ;)

There's a community wishlist entry for that too:
Add Turkish Lira to your list of local currencies.

And several duplicates:
Shopping with Turkish Liras
Regional Currency Support for Turkish Liras
GOG Team please add more localized currencies (Turkish Lira etc.)
Local Pricing for the Republic of Turkey and Turkish Lira Support
Adding Turkish lira to payment options
Turkish currency support and GOG Wallet

And there's an entry for translating the site as well:
Add Turkish language option on GOG

Maybe when you purge the Steam fanboys among you.

Then, the answer is clearly "never" ¯\_(ツ)_/¯