Develop a Keyboard App for Android and IOS in flutter

We need a special custom Keypad app for android and ios. You please have to develop the UI and the app itself. Its okay if it is in flutter / dart. The keyboard should be easy to install for the customer and should have three tabs with different functions.

We could use the google standard keayboard for input to have the user select the languages they need. The app should be translated in several languages. Its important that the app is stable. We need one in app purchase.