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).