I'm using macOS High Sierra (10.13.6) on a MacBook Pro 15. In the Keyboard Preferences pane, I have "Show keyboard and emoji viewers in menu bar" option in the "Keyboard" tab turned on:
Sure enough, as desired, there's a menubar icon that, when clicked shows these in a menu:
Here's the strange thing: sometimes that icon is the "window with command key icon" icon:
and sometimes it's a US flag:
When it's a flag, clicking it turns it back to the "window with command key icon" icon, and shows the previous menu.
My guess is that this is triggered by my having the "Show Input menu in menu bar" option in the Keyboard Preferences' "Input Sources" tab turned on:
If I turn "Show keyboard" off and leave "Show Input menu" on, then the icon stays a US Flag, and reliably shows an input menu:
So: any idea why these two menus can't coexist, and that the "Show viewers" option (mostly) overrides the "Input sources" optoin? Is this a macOS bug?