I use the Gnome extension Lock Keys. My keyboard doesn't have Numlock or other indicators, so it's very useful. Then I remembered that Windows displays an indicator in the center of the screen when I switch IME states. I'm looking for a similar feature but can't find it, so if anyone knows of one, please let me know.
I tried using Customize IBus, but something is wrong such as the indicators are misaligned or appear too often.