Cross-Platform Educational App

I am looking for App developers to take over an ongoing project.

I have an educational app that teachers users new English words. The app uses a mnemonic device to help students memorize new words. The concept for the app is as follows. The user already knows some basic English words and they use the words they already know to learn new ones. For example, the user knows the words 'create' and 'chair' so I use them to teach the word 'creature'. I then take these three words and make an animated story to help the user remember the definition of the word 'creature'. The user then reviews the word in many ways to help them remember it forever.

For this project I am looking to change the app to make it a global version.

This will entail the following...
A language menu where the user can choose the language they speak.
The ability to change language data in the backend.
5 languages needed to add to the app - Hindi, Bengali, Spanish, Portuguese and Mandarin.
There is currently a Wechat login. I need this to be changed to Android and IOS (for each version of the app)
SMS gateway that will be appropriate for a global user base.
Some minor changes to the tutorial portion of the app.
Payment gateways that are appropriate for global users.
Adding video adds to the free portion of the app.
Help putting the app on the Apple and Google play stores.

Please see screenshots to give you an idea of the app and it's scope.

I look forward to hearing from you so we can discuss this project further.