The devil is in the details and nowhere is this more true than UI design, but Apple, from time to time, beg to differ.
In older macOS/OS X versions, Apple used country flag icons to identify input sources and keyboard layout. It was a good UI design that led to good UX. The tiny multicolor flags on the top right of the screen were perfect for indicating the active input language.

In macOS Monterey 12.4, Apple replaced the flag icons with monochrome square icons containing letters that indicate the language. This wasn’t ideal for a lot of macOS users to say the least. The change took away something that worked perfectly well and replaced it with something that was seemingly much less refined.

Luckily, the “there is an app for that” saying is still true for macOS, or for this particular situation at least.
In fact, there are quite a few apps that will allow users to once again use flag icons instead of letters to indicate input language.
One of those apps is Keyboard Switcheroo.

Keyboard Switcheroo
Keyboard Switcheroo is a nice little app that allows you to use flags, emojis or even custom images to indicate the input language. The app lives in the menu bar, and it can also be a floating menu, a dock icon or even a desktop widget. It’s a perfect substitute for the default macOS input language selector especially when it lives in the menu bar.

At the time of this post, the app sells for $1.99 and has 4.9 stars from 16 ratings. The developer was responsive to email inquiries too and that was a plus.
Check out this link for more app reviews and recommendations, including Mini Calendar for macOS.