i use tixati on kde (linux)
i cant see the bottom of tixati setting window so i cant set font in setting.

Have the same problem and I actually requested in a post that they make this window adjustable in  a future update.  In the mean time, try and decrease your display settings to its smallest value, restart for it to take effect, and re-open Tixati. After you finished, reset your display settings. It worked for me, the window was smaller but fit well in the screen. It's not a good long term solution but a decent workaround in the short term.