Locales don't seem to work for GNOME Boxes in org.gnome.Platform//3.30
GNOME Boxes has some dysfunctional localization when run against the 3.30 runtime, but it works just fine when run against the "master" version of the runtime. For instance:
flatpak run --env=LC_ALL=de_DE.utf8 --runtime=org.gnome.Platform//3.30 org.gnome.Boxes
It works if I run it with:
flatpak run --env=LC_ALL=de_DE.utf8 --runtime=org.gnome.Platform//master org.gnome.Boxes
I maintain Boxes and nothing in regard of i18n support has changed since 3.26.