Quick i18n Checklist:

• All user-facing strings externalized
• No hardcoded text in code
• Date/time/currency formatted per locale
• RTL languages flip layout correctly
• Unicode characters display properly

Critical Success Factors:

• Don't hardcode strings - externalize everything
• Test with real speakers, not just translation files
• RTL requires mirrored UI layout

Quick Reference Card

When to Use

• Launching in new markets
• Adding language support
• Before international releases
• After UI changes

i18n vs l10n

Common Locale Formats

Translation Coverage Testing

test('all strings are translated', () => {
  const enKeys = Object.keys(translations.en);
  const frKeys = Object.keys(translations.fr);
  const esKeys = Object.keys(translations.es);

  // All locales have same keys
  expect(frKeys).toEqual(enKeys);
  expect(esKeys).toEqual(enKeys);
});

test('no missing translation placeholders', async ({ page }) => {
  await page.goto('/?lang=fr');
  const text = await page.textContent('body');

  // Should not see placeholder keys
  expect(text).not.toContain('translation.missing');
  expect(text).not.toMatch(/\{\{.*\}\}/); // {{key}} format
});

Date/Time/Currency Formats

test('date formats by locale', () => {
  const date = new Date('2025-10-24');

  expect(formatDate(date, 'en-US')).toBe('10/24/2025');
  expect(formatDate(date, 'en-GB')).toBe('24/10/2025');
  expect(formatDate(date, 'ja-JP')).toBe('2025/10/24');
});

test('currency formats by locale', () => {
  const amount = 1234.56;

  expect(formatCurrency(amount, 'en-US', 'USD')).toBe('$1,234.56');
  expect(formatCurrency(amount, 'de-DE', 'EUR')).toBe('1.234,56 €');
  expect(formatCurrency(amount, 'ja-JP', 'JPY')).toBe('¥1,235');
});

RTL (Right-to-Left) Testing

test('layout flips for RTL languages', async ({ page }) => {
  await page.goto('/?lang=ar'); // Arabic

  const dir = await page.locator('html').getAttribute('dir');
  expect(dir).toBe('rtl');

  // Navigation should be on right
  const nav = await page.locator('nav');
  const styles = await nav.evaluate(el =>
    window.getComputedStyle(el)
  );
  expect(styles.direction).toBe('rtl');
});

test('icons/images appropriate for RTL', async ({ page }) => {
  await page.goto('/?lang=he'); // Hebrew

  // Back arrow should point right in RTL
  const backIcon = await page.locator('.back-icon');
  expect(await backIcon.getAttribute('class')).toContain('rtl-flipped');
});

Unicode Character Support

test('supports unicode characters', async ({ page }) => {
  // Japanese
  await page.fill('#name', '山田太郎');
  await page.click('#submit');

  const saved = await db.users.findOne({ /* ... */ });
  expect(saved.name).toBe('山田太郎');

  // Arabic
  await page.fill('#name', 'محمد');
  // Emoji
  await page.fill('#bio', '👋🌍');

  expect(saved.bio).toBe('👋🌍');
});

Agent-Driven Localization Testing

// Comprehensive localization validation
await Task("Localization Testing", {
  url: 'https://example.com',
  locales: ['en-US', 'fr-FR', 'de-DE', 'ja-JP', 'ar-SA'],
  checks: ['translations', 'formats', 'rtl', 'unicode'],
  detectHardcodedStrings: true
}, "qe-test-generator");

// Returns:
// {
//   locales: 5,
//   missingTranslations: 3,
//   formatIssues: 1,
//   rtlIssues: 0,
//   hardcodedStrings: ['button.submit', 'header.title']
// }

Agent Coordination Hints

Memory Namespace

aqe/localization-testing/
├── translations/*       - Translation coverage
├── formats/*            - Locale-specific formats
├── rtl-validation/*     - RTL layout checks
└── unicode/*            - Character encoding tests

Fleet Coordination

const l10nFleet = await FleetManager.coordinate({
  strategy: 'localization-testing',
  agents: [
    'qe-test-generator',   // Generate l10n tests
    'qe-test-executor',    // Execute across locales
    'qe-visual-tester'     // RTL visual validation
  ],
  topology: 'parallel'
});

Related Skills

• accessibility-testing - Language accessibility
• compatibility-testing - Cross-platform i18n
• visual-testing-advanced - RTL visual regression

Remember

Don't hardcode. Externalize all user-facing strings. Every string visible to users must come from translation files, not code.

Test with native speakers, not just translation files. Machine translations and translation files can have context issues that only native speakers catch.

With Agents: Agents validate translation coverage, detect hardcoded strings, test locale-specific formatting, and verify RTL layouts automatically across all supported languages.