There is another post with the same issue here: Turkish Localization Error (Capital “I” Letter) - Bug Reports - Last Epoch Forums But since it has been closed, I had to create this post stating the same issue.
Screenshot: Imgur: The magic of the Internet
Above sample shows that even on the main menu there are lots of font failures. There are even much more in-game.
As I am a player who gives strong importance to visual consistency, this issue really drives me to refund the game.
Hm. Odd, have you already tried to verify your game files?
Yes, I have. Sadly, nothing changed 
Well, thank you; I have just refunded the game. I’m going to buy it again when it gets out of early access.
I think the problem happens because you haven’t manually default the culture to en-US. Hope you’ll do it before the full release. Good luck guys.
We investigated but we are not sure the cause of this problem, it is most likely only happening for Turkish users. The issue is logged internally and if we find a solution we will address the problem as quickly as we can.
Take care.