Several of our own translations of the Windows installer are unused
because Inno Setup corresponding translations are marked "unofficial".
This mostly means that the language files for these are probably old and
unmaintained, hence outdated. And these files are not bundled together
with Inno Setup release (though still hosted in their repo).

Nevertheless it doesn't make sense that we would just waste the work of
our translators here. Maybe Inno Setup localization is not complete, so
what? At best it could even encourage translators to contribute upstream
to Inno Setup. Let's just enable all our current localizations of the
installer and see how it goes!