Having already tested this approach with my son by making a similar desktop app, when he learned all the letters in a couple of hours, I wanted to port the same concept to the mobile phones. I made thirty pencil drawings (one for each letter of the Cyrillic alphabet), vectorized and colored them in Illustrator, and made the working prototype in Invision. I did the sound recording and editing (my wife read the text), and coded the app in React Native. I also created a website with a simple landing page announcing the publication of the app. React Native being a cross-platform library, the app can work both on iOS and Android.