AD-15 The OS is multi-lingual

Every word a person reads is translatable, and a language is added by adding a message catalog, never by changing a component. The platform's own chrome (desktop, console, Keycloak's pages) carries a message catalog per locale and no inline user-visible string; a component's catalog text carries a required fallback plus an optional map keyed by locale (de_DE, en_US). Matching is forgiving within a language and never across one (de-CH is served de_DE); a string with no translation renders its fallback, never a blank or a key. The viewer's language comes from their account, and from the browser until they have said.