Q:

Is it possible to develop mobile keyboard app in react native

we want to develop mobile keyboard app - (Third party keyboard) that have some unique features (such translate on the keyboard).
We would like to know if there is a way to developed it once both for IOS and Android, with React native, or any other solution? 
Thank !

A:

Short answer: no, it can only be developed in native code (java/android, Objective-C or Swift/iOS)
Long answer: React Native would be an overkill in this case since it would bring a lot of features which cannot be used by a custom keyboard. For example, all the List components or Navigation which are quite heavy. 
If you want to build a custom keyboard I would recommend to read the tutorials for iOS and Android about this matters: 

https://developer.apple.com/library/content/documentation/General/Conceptual/ExtensibilityPG/CustomKeyboard.html 
https://developer.android.com/guide/topics/text/creating-input-method.html

This pieces of functionality are really simple to develop so not a lot needs to be learned, plus having to maintain two codebases is not going to be a big overhead

