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Remarks

It says the page is missing, never that the learner's language is unsupported — and that distinction is the reason this file changed.

The proxy normalizes any first segment that is not a configured locale into a path under the default locale: /xx is answered with a 307 to /en/xx, /de/courses with a 307 to /en/de/courses. So a request never arrives here carrying an unsupported locale. Every request that reaches this page has a supported locale and a path that matches no route, which is why the page's earlier "Locale not supported" copy was wrong in every case it was ever shown — including /es/error, where it told a Spanish reader that Spanish was unavailable.

A path that bypasses the proxy — /manifest.json, excluded from its matcher along with every other dotted path — is turned away by requireSupportedLocale before any locale context exists, and resolves to the framework's own not-found page above this boundary. There is no locale to localize a message into there, and the requester is a machine.

Both links go through @/i18n/navigation, so they keep the active locale: the request already told us the learner's language, and discarding it would be a second small failure on top of the first.

The course lobby is offered to everyone, and the page reads no session to decide it. A visitor without one is taken through sign-in and back, as on every other personal route; looking the session up here would cost a second auth and database read on every missing page, for a secondary link.

The state sits on the header's content column rather than in a card, and takes every colour from the theme tokens, so it follows the light and dark variants like the pages around it.

Spec: lesson-view-polish § "An unknown path under a supported locale renders a localized Page Not Found", § "The Page Not Found state offers the course lobby as a second way out" and § "The Page Not Found state wears the Immersion Cinema theme".