Switch language in place, without a reload

Choosing a language in the picker now applies it at once. The choice is
stored and ?lang is kept in step through replaceState, and the picker keeps
focus.

Code that writes translated text itself re-presents it on a switch:
onLocaleChange() lets an owner listen, removed at teardown, and status
writers hand over a function of the locale (voice cards, scene director,
SDR, draw hints, imagery split, map sources, Bhote Koshi media) so the
words are rebuilt rather than re-sent. The HUD, cockpit, radio, CCTV,
launch, awareness and credit texts follow the same hook, and
applyDocumentTranslations can be applied again without undoing text code
wrote since.

The unsaved-work registry and persistLocaleAndReload existed only to guard
the reload, so they go, with their catalog entries.

src/layers/awareness/panel.js

@@ -2,7 +2,12 @@ import {
   formatAwarenessLabel,
   AWARENESS_RADIUS_M,
 } from '../../data/militaryAwarenessEngine.js';
-import { formatNumber, t, translateKnown } from '../../i18n/index.js';
+import {
+  formatNumber,
+  onLocaleChange,
+  t,
+  translateKnown,
+} from '../../i18n/index.js';
 import { formatQuantity } from '../../ui/unitLabels.js';
 import { AWARENESS_PAGE_SIZE, AWARENESS_PAGE_ROTATE_MS } from './policy.js';
 
@@ -73,6 +78,12 @@ export function createPanel({ state: layerState, parts }) {
   /** The panel shows layer views from the first enable or result onwards. */
   function ensurePanel() {
     layerState.panelShown = true;
+    // A shown view is worded again in a new locale.
+    layerState.offPanelLocale ??= onLocaleChange(() => {
+      const kind = layerState.panelView?.kind;
+      if (kind === 'results') renderResults();
+      else if (kind === 'standby') hidePanel();
+    });
   }
 
   function hidePanel() {
@@ -92,6 +103,8 @@ export function createPanel({ state: layerState, parts }) {
   /** Clear the panel when the layer is destroyed. */
   function clearPanel() {
     if (layerState.panelShown) publish({ kind: 'empty' });
+    layerState.offPanelLocale?.();
+    layerState.offPanelLocale = null;
     layerState.panelShown = false;
     layerState.panelView = null;
     layerState.panelSignature = '';

src/layers/launches/panel.js

@@ -1,5 +1,5 @@
 import * as Cesium from 'cesium';
-import { t } from '../../i18n/index.js';
+import { onLocaleChange, t } from '../../i18n/index.js';
 import {
   MISSION_CLOSE_VIEW_RANGE_M,
   MISSION_GLOBE_VIEW_RANGE_M,
@@ -436,12 +436,20 @@ export function createPanel({ state: layerState, services, parts, source }) {
         preview: scheduleMissionRosterPreview,
         clear: clearMissionRosterPreviewState,
       });
+    // The roster and mission are worded again in a new locale.
+    layerState._offMissionLocale = onLocaleChange(() => {
+      renderMissionRoster();
+      updateMissionTelemetry(true, false);
+      publishPanel();
+    });
     publishPanel();
   }
 
   /** Stop presenting; the components return to their initial markup. */
   function clearMissionPanel() {
     layerState._missionPanelReady = false;
+    layerState._offMissionLocale?.();
+    layerState._offMissionLocale = null;
     layerState._missionRosterPreviewOwnership = null;
     layerState._missionRosterView = null;
     layerState._missionRosterSignature = null;

src/layers/radio/presentation.js

@@ -1,3 +1,5 @@
+import { getLocale } from '../../i18n/index.js';
+
 export function createPresentation({
   state: layerState,
   services,
@@ -10,9 +12,26 @@ export function createPresentation({
     return layerState._acceptedCatalogSnapshot;
   }
 
+  /** Build the station categories, labelled in the current locale. */
+
+  function buildCategories() {
+    layerState._categories = Object.freeze(
+      parts.categories
+        .buildRadioCategories(layerState._stations)
+        .map((category) => Object.freeze(category)),
+    );
+    layerState._categoriesLocale = getLocale();
+  }
+
   /** Return an immutable snapshot consumed by the right-rail UI. */
 
   function getRadioUIState() {
+    // Labels follow a language switch the next time the state is read.
+    if (
+      layerState._categories.length &&
+      layerState._categoriesLocale !== getLocale()
+    )
+      buildCategories();
     const visible = parts.queries.visibleStations();
     const selected = parts.queries.selectedStation();
     return Object.freeze({
@@ -98,6 +117,7 @@ export function createPresentation({
   return {
     getRadioAcceptedCatalogSnapshot,
     getRadioUIState,
+    buildCategories,
     emitState,
     subscribeToRadio,
     subscribeToRadioPlaybackControls,

src/layers/radio/rendering.js

@@ -295,11 +295,7 @@ export function createRendering({
     layerState._stationById = new Map(
       stations.map((station) => [station.id, station]),
     );
-    layerState._categories = Object.freeze(
-      parts.categories
-        .buildRadioCategories(stations)
-        .map((category) => Object.freeze(category)),
-    );
+    parts.presentation.buildCategories();
     if (
       layerState._filter === DEFAULT_RADIO_FILTER &&
       !parts.categories.filterRadioStations(stations, DEFAULT_RADIO_FILTER)

src/layers/radio/state.js

@@ -38,6 +38,7 @@ export function createState({ services }) {
   layerState._stationById = new Map();
 
   layerState._categories = [];
+  layerState._categoriesLocale = null;
 
   layerState._renderById = new Map();