Hi Ramesh,
when you press the capslock button, the string within the variable layoutShiftOn gets loaded and applies the text / keys on the key buttons. This will overwritte the string that you have set.
What you could do for example is to create a dedicated button class which is derived from ExtendedVirtualKeyboard::Button. Inside your new button class you can add then a text view with the string 'English'.
Regards,
Julian