The gallery re-drove the visible tab by re-setting its profile-config, which works only for a map
that re-reads its whole config live. Two production maps do not: Big Picture resolves its tStatic
strings once (2 of 352 changed on en to ar, measured) and Simple Research copies its config into its
panes once (0 of 43, 0 of 105). A fresh element reads the new locale at mount, so the visible tab is
now rebuilt in the new language whatever the map does inside, the way a provider change rebuilds.
View state is lost on a language switch; that is accepted.
Hidden tabs that are still mounted (a light tab stays mounted when hidden, and select() never
remounts a mounted tab) are reset too, so their next open mounts in the new language. The old comment
said they picked it up lazily; for light tabs they did not. Tabs are reset in place, keeping the slot
ref, because a light pane renders once and releaseTab's deleted ref would never come back.
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