Language Input Selection Dialog shortcut I am using Catalina 10.15.3, and I am struggling to find the small dialog that is shown when switching between languages. That dialog showed all the input languages that I selected. Sometimes, I use apps in full screen and when I change the input language with shortcut I will need to reach the topbar with mouse so that I can see what language is being selected.

I am looking for that input language change dialog.

P.S. I am not sure about the word 'dialog'. It is a just a small window just pops in the middle of the screen and disappears in a couple of seconds.
Welcome to Ask Different. 

You could enable/set keyboard shortcuts for changing input sources. Go to System Preferences > Keyboard > Shortcuts settings, and in the left pane select Input sources. Then just enable the two command shortcuts for changing input sources. I've attached an image of what the settings looks like below. You can enable and/or change the shortcut to your liking. 



When I use the shortcut, the input sources dialog box shows as long as you hold down the shortcut keys (see image below). 



I'm doing all of this on macOS Mojave, but I think this works in Catalina too. Hope this helps!