frontend/angular/src/app/session-route-context.spec.ts

@@ -92,4 +92,14 @@ describe('session route context', () => {
     expect(hostRouteContextResolver(route({}, { lang: 'da-DK' }) as never, {} as never).locale).toBe('da');
     expect(playerRouteContextResolver(route({}, { lang: 'EN' }) as never, {} as never).locale).toBe('en');
   });
+
+  it('does not reset persisted preferred locale when lang query param is absent', () => {
+    const localStorage = storageMock({ 'wpp.locale': 'da' });
+    setWindow(localStorage, storageMock());
+
+    expect(hostRouteContextResolver(route({}, { lang: 'da' }) as never, {} as never).locale).toBe('da');
+    expect(hostRouteContextResolver(route({}, {}) as never, {} as never).locale).toBe('da');
+    expect(localStorage.setItem).toHaveBeenCalledTimes(1);
+    expect(localStorage.setItem).toHaveBeenCalledWith('wpp.locale', 'da');
+  });
 });

frontend/angular/src/app/session-route-context.ts

@@ -2,7 +2,7 @@ import { inject } from '@angular/core';
 import { type ActivatedRouteSnapshot, type CanActivateFn, type ResolveFn, Router, type UrlTree } from '@angular/router';
 
 import { createSessionContextStore } from '../../../src/spa/session-context-store';
-import { normalizeLocale, setPreferredLocale } from './lobby-i18n';
+import { normalizeLocale, resolvePreferredLocale, setPreferredLocale } from './lobby-i18n';
 
 export interface RouteSessionContext {
   sessionCode: string | null;
@@ -64,9 +64,14 @@ export function resolveSessionCode(route: ActivatedRouteSnapshot, mode: 'host' |
 }
 
 function resolveRouteLocale(route: ActivatedRouteSnapshot): string {
-  const locale = normalizeLocale(route.queryParamMap.get('lang'));
-  setPreferredLocale(locale);
-  return locale;
+  const langParam = route.queryParamMap.get('lang');
+  if (langParam !== null) {
+    const locale = normalizeLocale(langParam);
+    setPreferredLocale(locale);
+    return locale;
+  }
+
+  return resolvePreferredLocale();
 }
 
 async function sessionExists(code: string): Promise<boolean> {