For Apple iOS and Google Android, the Daily Readings Plus version does have the Fasting, Readings, Saints, and Paschalion in Greek. You can set the app to Greek by navigating to Settings and then changing “Title & Interface” and “Preferred Content” to Greek.
If you’re using the free or pay versions of the app, you can change the language for individual readings.
At this time, a few sections are only in English. In regards to the Prayers section - specifically in the iOS app - you are able to add your own prayers in Greek by tapping on the “+” button in the upper left hand corner, then pasting in your favorite prayers in Greek.