How do I change the language of halo wars 2 to Turkish?
From some internet skimming, the language of the game seems to be tied (for whatever reason) to the language your system is set to.
Try setting it to Turkish if you haven't already?
now system language is turkish but game is english
Halo Wars 2's language settings are tied to the profile that is currently signed in to the game. Are you using an Xbox or a PC?

Found this in the forums on an older post for PC. On xbox it will go by your set language on either the xbox or profile. I hope this helps!

The game choose it's UI language by looking up Windows' language list, located in [control panel\ clock, language and region\ language]. Put the language that you want the game to use at top.