This is the only "language" from the list whose name is special and
should be localized at runtime, yet before we set any Preferences
language. It needs to be localized as the System Language itself which
will be run-dependant.
For instance, if your system is in French, it will be displayed as
"Langue système" but if you change your system to Korean, at next run,
it would show "시스템 언어". It is a per-run localization, independant
from the language selected in Preferences, and even less dependant from
build-time system language.
Since localization is fully handled plug-in side now (see #8124), we
need to make sure the query functions are run again for all plug-ins
when the UI language changes (otherwise we might end up with
localizations from the previously used languages).
We were already reloading plug-ins when explicitly changing the lang in
the Preferences, but this new implementation is much better as it's
generic. In particular, it will also handle the case when the system
language changes (or when you play with locale environment variables).
Jehan