Making a mobile app for learning vocabulary

Hello, I would like to create an application for learning vocabulary of five most spoken languages in the world (such as English, Spanish, French, German, and Chinese)

In this application, some most usable words will be introduced daily.

Users can listen to the pronunciation of each word and then check off whether they have learned it.
I want this app to have a monthly subscription option.

Functional Android app
Functional IOS App
App Design
App submission
App icon
Splash screen
Ad network integration
Source code