feat(i18n): pick language from ?lang, saved choice or browser language

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/app/services/language-preference.service.spec.ts

@@ -0,0 +1,52 @@
+import { TestBed } from '@angular/core/testing';
+
+import { LanguagePreferenceService } from './language-preference.service';
+
+describe('LanguagePreferenceService', (): void => {
+  let service: LanguagePreferenceService;
+
+  beforeEach((): void => {
+    localStorage.clear();
+    window.history.replaceState(null, '', '/');
+    service = TestBed.inject(LanguagePreferenceService);
+  });
+
+  afterEach((): void => {
+    vi.restoreAllMocks();
+    window.history.replaceState(null, '', '/');
+  });
+
+  it('should fall back to English for unsupported browser languages', (): void => {
+    vi.spyOn(navigator, 'language', 'get').mockReturnValue('fr-FR');
+    expect(service.initialize()).toBe('en');
+  });
+
+  it('should use the browser language on the first visit', (): void => {
+    vi.spyOn(navigator, 'language', 'get').mockReturnValue('de-AT');
+    expect(service.initialize()).toBe('de');
+  });
+
+  it('should prefer a stored choice over the browser language', (): void => {
+    vi.spyOn(navigator, 'language', 'get').mockReturnValue('de-AT');
+    localStorage.setItem('portfolio-language', 'en');
+    expect(service.initialize()).toBe('en');
+  });
+
+  it('should prefer the lang query parameter over everything else', (): void => {
+    localStorage.setItem('portfolio-language', 'en');
+    window.history.replaceState(null, '', '/?lang=de');
+    expect(service.initialize()).toBe('de');
+  });
+
+  it('should ignore an unsupported lang query parameter', (): void => {
+    vi.spyOn(navigator, 'language', 'get').mockReturnValue('en-US');
+    window.history.replaceState(null, '', '/?lang=fr');
+    expect(service.initialize()).toBe('en');
+  });
+
+  it('should persist a confirmed language', (): void => {
+    service.confirmLanguage('de');
+    expect(service.languageCode()).toBe('de');
+    expect(localStorage.getItem('portfolio-language')).toBe('de');
+  });
+});

src/app/services/language-preference.service.ts

@@ -2,31 +2,35 @@ import { Injectable, signal } from '@angular/core';
 
 import type { LanguageCode } from '../../languages/language.types';
 
+const isLanguageCode = (value: string | null): value is LanguageCode =>
+  value === 'en' || value === 'de';
+
 @Injectable({ providedIn: 'root' })
 export class LanguagePreferenceService {
   private static readonly storageKey = 'portfolio-language';
   private readonly currentLanguageCode = signal<LanguageCode>('en');
-  private readonly languageConfirmed = signal(true);
 
   readonly languageCode = this.currentLanguageCode.asReadonly();
-  readonly isLanguageConfirmed = this.languageConfirmed.asReadonly();
 
-  initializeFromStorage(): LanguageCode {
+  /** Picks the language from `?lang=`, then the stored choice, then the browser language. */
+  initialize(): LanguageCode {
     if (typeof window === 'undefined') {
       return this.currentLanguageCode();
     }
 
-    const storedLanguage = window.localStorage.getItem(LanguagePreferenceService.storageKey);
-    if (storedLanguage === 'de' || storedLanguage === 'en') {
-      this.currentLanguageCode.set(storedLanguage);
-    }
+    const candidates = [
+      new URLSearchParams(window.location.search).get('lang'),
+      window.localStorage.getItem(LanguagePreferenceService.storageKey),
+      window.navigator.language.slice(0, 2).toLowerCase(),
+    ];
+    const language = candidates.find(isLanguageCode) ?? 'en';
+    this.currentLanguageCode.set(language);
 
-    return this.currentLanguageCode();
+    return language;
   }
 
   confirmLanguage(code: LanguageCode): void {
     this.currentLanguageCode.set(code);
-    this.languageConfirmed.set(true);
 
     if (typeof window !== 'undefined') {
       window.localStorage.setItem(LanguagePreferenceService.storageKey, code);

src/app/services/language.service.ts

@@ -2,26 +2,15 @@ import { Injectable, computed, inject } from '@angular/core';
 
 import { deLanguage } from '../../languages/de';
 import { enLanguage } from '../../languages/en';
-import type { LanguageCode, LanguagePack } from '../../languages/language.types';
+import type { LanguagePack } from '../../languages/language.types';
 import { LanguagePreferenceService } from './language-preference.service';
 
+/** Page content for the lazy-loaded routes; kept apart from the shell texts to stay out of the initial bundle. */
 @Injectable({ providedIn: 'root' })
 export class LanguageService {
-  private readonly languagePreferenceService = inject(LanguagePreferenceService);
+  private readonly languageCode = inject(LanguagePreferenceService).languageCode;
 
-  readonly languageCode = this.languagePreferenceService.languageCode;
-  readonly isLanguageConfirmed = this.languagePreferenceService.isLanguageConfirmed;
-  readonly content = computed<LanguagePack>(() => this.getPack(this.languageCode()));
-
-  initializeFromStorage(): LanguageCode {
-    return this.languagePreferenceService.initializeFromStorage();
-  }
-
-  confirmLanguage(code: LanguageCode): void {
-    this.languagePreferenceService.confirmLanguage(code);
-  }
-
-  getPack(code: LanguageCode): LanguagePack {
-    return code === 'de' ? deLanguage : enLanguage;
-  }
+  readonly content = computed<LanguagePack>(() =>
+    this.languageCode() === 'de' ? deLanguage : enLanguage,
+  );
 }

src/app/services/shell-language.service.ts

@@ -6,20 +6,10 @@ import { LanguagePreferenceService } from './language-preference.service';
 
 @Injectable({ providedIn: 'root' })
 export class ShellLanguageService {
-  private readonly languagePreferenceService = inject(LanguagePreferenceService);
+  private readonly languageCode = inject(LanguagePreferenceService).languageCode;
 
-  readonly languageCode = this.languagePreferenceService.languageCode;
-  readonly isLanguageConfirmed = this.languagePreferenceService.isLanguageConfirmed;
   readonly content = computed<LanguageShellPack>(() => this.getPack(this.languageCode()));
 
-  initializeFromStorage(): LanguageCode {
-    return this.languagePreferenceService.initializeFromStorage();
-  }
-
-  confirmLanguage(code: LanguageCode): void {
-    this.languagePreferenceService.confirmLanguage(code);
-  }
-
   getPack(code: LanguageCode): LanguageShellPack {
     return code === 'de' ? deShellLanguage : enShellLanguage;
   }