Implement safe storage utility and update i18n handling to use it

src/tests/i18n-resilience.test.ts

@@ -0,0 +1,54 @@
+import { describe, it, expect, vi, beforeEach } from 'vitest';
+
+const blockStorage = () => {
+  Object.defineProperty(window, 'localStorage', {
+    configurable: true,
+    get() {
+      throw new DOMException('The operation is insecure.', 'SecurityError');
+    },
+  });
+};
+
+const failLocaleFetches = () => {
+  vi.stubGlobal(
+    'fetch',
+    vi.fn(() => Promise.reject(new TypeError('NetworkError')))
+  );
+};
+
+describe('i18n resilience on hardened browsers', () => {
+  beforeEach(() => {
+    vi.resetModules();
+    vi.unstubAllGlobals();
+  });
+
+  it('getLanguageFromUrl does not throw when localStorage access is blocked', async () => {
+    blockStorage();
+    const { getLanguageFromUrl } = await import('../js/i18n/i18n');
+    expect(() => getLanguageFromUrl()).not.toThrow();
+    expect(getLanguageFromUrl()).toBe('en');
+  });
+
+  it('initI18n succeeds with blocked storage and failing locale fetches', async () => {
+    blockStorage();
+    failLocaleFetches();
+    const { initI18n, t } = await import('../js/i18n/i18n');
+    await expect(initI18n()).resolves.toBeDefined();
+    expect(t('simpleMode.title')).not.toBe('simpleMode.title');
+  });
+
+  it('t() serves bundled English instead of raw keys when fetches fail', async () => {
+    failLocaleFetches();
+    const { initI18n, t } = await import('../js/i18n/i18n');
+    await initI18n();
+    expect(t('simpleMode.title')).toBe('PDF Tools');
+    expect(t('tools:pdfToTiff.name')).toBe('PDF to TIFF');
+    expect(t('common.error')).not.toBe('common.error');
+  });
+
+  it('changeLanguage does not throw when storage is blocked', async () => {
+    blockStorage();
+    const { changeLanguage } = await import('../js/i18n/i18n');
+    expect(() => changeLanguage('de')).not.toThrow();
+  });
+});