Created attachment 134319 [details]
Reginal settings

SUMMARY
For example reginal formats to "uz_UZ", which is not generated, and results in this regional settings set to C.UTF-8:
```
❯ locale
LANG=C.UTF-8
LANGUAGE=ru:en_US:en_GB:uk
LC_CTYPE="C.UTF-8"
LC_NUMERIC=C.UTF-8
LC_TIME=C.UTF-8
LC_COLLATE=C.UTF-8
LC_MONETARY=C.UTF-8
LC_MESSAGES="C.UTF-8"
LC_PAPER=uk_UA.UTF-8
LC_NAME=uk_UA.UTF-8
LC_ADDRESS=uk_UA.UTF-8
LC_TELEPHONE=uk_UA.UTF-8
LC_MEASUREMENT=C.UTF-8
LC_IDENTIFICATION=uk_UA.UTF-8
LC_ALL=
```

This setup breaks opening archives from dolphin (see ark attachment)

STEPS TO REPRODUCE
1. Go to kcm language settings.
2. Set regional settings to ones with no generated locale.
3. Enjoy C.UTF-8

OBSERVED RESULT
KDE does not warn when switching regional locales to ones with no generated locale available.

EXPECTED RESULT
KDE should warn user when switching regional locales to ones with no generated locale available.

SOFTWARE/OS VERSIONS
Windows: 
macOS: 
Linux/KDE Plasma: Kubuntu 20.10
(available in About System)
KDE Plasma Version: 5.19.5
KDE Frameworks Version: 5.74.0
Qt Version: 5.14.2

ADDITIONAL INFORMATION