More about this
http://steamcommunity.com/app/221100/discussions/0/540744934485524132/?l=german

Isn't the steamcommunity discussion about people failing to set the User Interface resolution to a rather normal resolution (1920x1080), which should be possible under normal circumstances. ( http://i.imgur.com/JJ2fMvW.jpg )
Im not sure if UHD should be avalible there atm, if you have the right Screen, but i'm sure it will be, when higher resolution displays become more common (or the DX11 rederer gets implemented).
Until then you have the workaround in DayZ.cfg
Resolution_W=XXXX;
Resolution_H=YYYY;

Hello neti_netwalker,

If you go to Configure --> Video --> User Interface and select your screen resolution from the dropdown list, you should get prompted to restart the game after backing out towards the main menu. Afterwards you should be able to go to Configure --> Video and then change "Rendering Resolution" to match your screen resolution.

Since the button labels might not be legible in your game due to the current User Interface resolution, you can use the following link to see which buttons to click: http://i.imgur.com/o5hWeoy.jpg

Regards,

JStewart