Replace all String literals with references to String resources
Currently most text in the app (messages, information, etc) uses String literals. This is not a recommended practice for Android development. Rather, all strings should be defined in res/values/strings.xml. This is to make localization much easier. That means every single place in the app that uses String literals should be refactored. For example, a Toast called by
Toast.makeText(getContext(), "Notifications set.", Toast.LENGTH_SHORT) should instead be called by
Toast.makeText(getContext(), getString(R.id.notification_set_string), Toast.LENGTH_SHORT).