I recently changed how overridden translations are loaded. It’s possible that there’s a bug somewhere, but I can’t reproduce it right now.
I set the default_locale to “svenska” and saw “Webbplatsinställningar”. After setting admin_js.admin.site_settings.title to “Inställningar” and reloading the page it correctly showed “Inställningar” everywhere.
What do you see when you load https://discourse.example.com/extra-locales/overrides in your browser? I see the following:
I18n._mfOverrides = {};
I18n._overrides = {"admin_js.admin.site_settings.title":"Inställningar"};