As someone learning Japanese, that seems very much like an app I would want and love. I hope you are able to sort this out soon so I can buy it!
Also Igor, if you are reading this, your GitHub and LinkedIn icons in your sites header link to GitHub and LinkedIn's homepages rather than your profiles. Probably want to fix that ;)
I managed to create a completely new Apple id and get through, if you are interested in testing the app and providing feedback you can join Testlflight beta https://testflight.apple.com/join/SHngHsGk
Also Igor, if you are reading this, your GitHub and LinkedIn icons in your sites header link to GitHub and LinkedIn's homepages rather than your profiles. Probably want to fix that ;)