Currently, --serverinfo requires users to specify Qt Country IDs. This is not user-friendly.
With Qt6, --serverinfo will require users to specify Qt5 Country IDs, even if they are on Qt6. This is really not user-friendly.

Has this feature been discussed and generally agreed?

The ugliness of the status quo, especially when adding support for Qt6, has been officially stated by @pljones here: #2299 (review) :)

Describe the solution you'd like

--serverinfo should support ISO country codes, e.g. --serverinfo 'FooServer;FooCity;de
We should still keep support for the numerical IDs for compatibility.