Bug 504520

SUMMARY
After updating from 6.3.5 to 6.4 beta, plasmashell started using one cpu core at 100% and spamming the log with: `kf.i18n.qml: No QML engine available, KLocalizedQmlContext not properly set up?`

STEPS TO REPRODUCE
I don't know, a user account created on an older version of plasma with untouched settings works without problems on plasma 6.4 beta.

OBSERVED RESULT
Plasma spams the user journal with `kf.i18n.qml: No QML engine available, KLocalizedQmlContext not properly set up?` and uses 100% on one cpu core.

EXPECTED RESULT
Even if the locale settings are wonky, plasma should probably fallback to "C" locale and not hog the cpu.


SOFTWARE/OS VERSIONS
Operating System: Arch Linux 
KDE Plasma Version: 6.3.90
KDE Frameworks Version: 6.14.0
Qt Version: 6.9.0
Kernel Version: 6.14.6-arch1-1 (64-bit)
Graphics Platform: Wayland
Processors: 24 × AMD Ryzen 9 7900X 12-Core Processor
Memory: 96 GiB of RAM (93.5 GiB usable)
Graphics Processor 1: AMD Radeon RX 7700 XT
Graphics Processor 2: AMD Radeon Graphics

ADDITIONAL INFORMATION
I suspect some issue with the user locale config, but my /etc/locale.conf is properly configured:
LANGUAGE=en_US.UTF-8
LANG=en_US.UTF-8
LC_CTYPE=en_US.UTF-8
LC_NUMERIC=en_US.UTF-8
LC_TIME=en_US.UTF-8
LC_COLLATE=en_US.UTF-8
LC_MONETARY=en_US.UTF-8
LC_MESSAGES=en_US.UTF-8
LC_PAPER=en_US.UTF-8
LC_NAME=en_US.UTF-8
LC_ADDRESS=en_US.UTF-8
LC_TELEPHONE=en_US.UTF-8
LC_MEASUREMENT=en_US.UTF-8
LC_IDENTIFICATION=en_US.UTF-8
LC_ALL=en_US.UTF-8

~/.config/plasma-localerc contains:
[Formats]
LANG=en_US.UTF-8
LC_ADDRESS=de_DE.UTF-8
LC_MEASUREMENT=en_IE.UTF-8
LC_MONETARY=en_IE.UTF-8
LC_NAME=de_DE.UTF-8
LC_PAGE=en_US.UTF-8
LC_PAPER=en_IE.UTF-8
LC_TELEPHONE=de_DE.UTF-8
LC_TIME=en_IE.UTF-8

/etc/locale.gen contains the correct entries for "de_DE.UTF-8", "en_US.UTF-8" and "en_IE.UTF-8"
and I even went through the Region & Languages settings and reconfigured the locales.