Quite obviously you never interacted with any software which defaults to the language you can't read, despite having a support for the language you do understand.
How would flags in the language selection help? The actual problem is finding the language selection at all (which still has an icon of a (stylised) globe on MacOS).
Language select used to have a flag of current language. Political correctness might have made companies change that convention making it hard to find as you say, but it used to be that you looked for flags to find the language setting.
I remember windows having flags for the languages, but now it is a strange A symbol that I have no clue what it is and I'd have no chance of finding if it was in the wrong language.