All great answers. But in Swift you can override methods and variables defined in parent class (UIResponder) in an extension. So it's not necessary to subclass. And it's nice to replace the for loop with a more swift like one-liner.
public extension UITextField { override var textInputMode: UITextInputMode? { return UITextInputMode.activeInputModes.filter { $0.primaryLanguage == "emoji" }.first ?? super.textInputMode }}Instead of "emoji" probably will be something like Utils.currentAppLanguage