Custom Russian Keyboard Layouts
Apple has long provided English keyboard layouts with an ABC icon for English speakers who prefer not to have the US or other country flag in the top right corner of their screen all the time.
Russian is also used by a very large number of people outside that country who may prefer a flagless or other national icon when using the Input Source for that language.
Here you can find a set of Russian language keyboards that have a generic Cyrillic "Я" icon instead of a national flag.
To install, put the .bundle file in /Library/Keyboard Layouts or Home/Library/Keyboard Layouts and then activate the keyboard via System Preferences > Keyboard > Input Sources > + .
For a Russian layout with a Ukrainian flag icon, see this page.