How do you add the Language Icon to a MacBook Pro desktop menu?

You can add the language icon yourself to the menu bar, it has not been removed in any way.

Its always been an option you add or remove from the menu bar yourself.

Go to System Settings ➜ Keyboard ➜ Text Input ➜ Input Sources ➜ [Edit] ➜ Show Input Menu in Menu Bar and make sure its toggled on.

Quillnib wrote: How do you add the language icon to your desktop so that you can quickly switch back and forth between more than one language while writing emails?

In addition to the input menu at the top right of the screen, you can switch keyboards via Fn/Globe or Control Space. See

Write in another language on Mac - Apple Support

Be sure that you have the keyboards you want on your Input Source list. For English it should be US or ABC or British. The Preferred Language list is not relevant to keyboards, it governs the language of the MacOs user interface.