Do I need to register account in order to use Keyboard Extension?
No, you do not need to create account in order to use basic features of Keyboard Extension.
Nonetheless, you would need to register account and authenticate in order to create your own layouts and plugins. Account holders also enjoy access to more layouts and plugins.
Once you have an account, you will be able to access Layout Editor integrated into Android app enabling you to create your own layouts.
In order to register you would need email address only.