Untranslatable strings (due to missing i18n infrastructure for libgnome-volume-control?)
https://gitlab.gnome.org/GNOME/libgnome-volume-control/blob/master/gvc-mixer-control.c includes two translatable strings:
return g_strdup (_("Disabled"));
gvc_mixer_stream_set_name (stream, _("System Sounds"));
but I don't see any way to translate them, like a /po subfolder or https://l10n.gnome.org/module/libgnome-volume-control/
See https://wiki.gnome.org/TranslationProject/DevGuidelines or ask on https://mail.gnome.org/mailman/listinfo/gnome-i18n