Created attachment 144919 [details]
Region selection

SUMMARY
en_MY locale is shown in Region selection, but it does not exists in locale.gen (only ms_MY does). As a result

STEPS TO REPRODUCE
1. Navigate to Region selection
2. Note that ms_MY is listed twice.
3. Select "Malaysia - English (en_MY)". Save, reboot

OBSERVED RESULT
[user@T490x ~]$ locale
locale: Cannot set LC_CTYPE to default locale: No such file or directory
locale: Cannot set LC_MESSAGES to default locale: No such file or directory
locale: Cannot set LC_ALL to default locale: No such file or directory
LANG=en_MY.UTF-8
LC_CTYPE="en_MY.UTF-8"
LC_NUMERIC=ru_RU.UTF-8
LC_TIME=en_GB.UTF-8
LC_COLLATE="en_MY.UTF-8"
LC_MONETARY=ms_MY.UTF-8
LC_MESSAGES="en_MY.UTF-8"
LC_PAPER=en_DK.UTF-8
LC_NAME=en_DK.UTF-8
LC_ADDRESS=en_DK.UTF-8
LC_TELEPHONE=en_DK.UTF-8
LC_MEASUREMENT=C
LC_IDENTIFICATION=en_DK.UTF-8
LC_ALL=

[user@T490x ~]$ perl
perl: warning: Setting locale failed.
perl: warning: Please check that your locale settings:
LANGUAGE = "en_US:en_GB:ru",
LC_ALL = (unset),
LC_ADDRESS = "en_DK.UTF-8",
LC_NAME = "en_DK.UTF-8",
LC_MONETARY = "ms_MY.UTF-8",
LC_PAPER = "en_DK.UTF-8",
LC_IDENTIFICATION = "en_DK.UTF-8",
LC_TELEPHONE = "en_DK.UTF-8",
LC_MEASUREMENT = "C",
LC_TIME = "en_GB.UTF-8",
LC_NUMERIC = "ru_RU.UTF-8",
LANG = "en_MY.UTF-8"
are supported and installed on your system.
perl: warning: Falling back to the standard locale ("C").

EXPECTED RESULT
No errors shown

SOFTWARE/OS VERSIONS

Linux/KDE Plasma:
(available in About System)
KDE Plasma Version: 5.23.4 
KDE Frameworks Version: 5.89.0
Qt Version: 5.15.2

ADDITIONAL INFORMATION
I believe it is a common issue for all previous versions of KDE.