feat(i18n): add Russian (ru) localization support (#798)

tests/e2e/language-russian.spec.ts

@@ -0,0 +1,92 @@
+import { closeElectronApp, expect, getStableWindow, test } from './fixtures/electron';
+
+test.describe('Russian language localization', () => {
+  test('shows Russian language option in setup wizard', async ({ launchElectronApp }) => {
+    const app = await launchElectronApp();
+    
+    try {
+      const page = await getStableWindow(app);
+      
+      // Should see the setup wizard
+      await expect(page.getByTestId('setup-page')).toBeVisible();
+      
+      // Should have Russian language button visible
+      const russianButton = page.locator('button', { hasText: 'Русский' });
+      await expect(russianButton).toBeVisible();
+    } finally {
+      await closeElectronApp(app);
+    }
+  });
+
+  test('can switch to Russian language in setup wizard', async ({ launchElectronApp }) => {
+    const app = await launchElectronApp();
+    
+    try {
+      const page = await getStableWindow(app);
+      
+      await expect(page.getByTestId('setup-page')).toBeVisible();
+      
+      // Click Russian language button
+      const russianButton = page.locator('button', { hasText: 'Русский' });
+      await russianButton.click();
+      
+      // Verify UI renders in Russian by checking for Russian-only text
+      // "Добро пожаловать" is unique to Russian and won't appear in English
+      await expect(page.locator('h2')).toContainText('Добро пожаловать');
+    } finally {
+      await closeElectronApp(app);
+    }
+  });
+
+  test('Russian language persists after skipping setup', async ({ launchElectronApp }) => {
+    const app = await launchElectronApp();
+    
+    try {
+      const page = await getStableWindow(app);
+      
+      await expect(page.getByTestId('setup-page')).toBeVisible();
+      
+      // Switch to Russian
+      const russianButton = page.locator('button', { hasText: 'Русский' });
+      await russianButton.click();
+      
+      // Skip setup
+      await page.getByTestId('setup-skip-button').click();
+      await expect(page.getByTestId('main-layout')).toBeVisible();
+      
+      // Navigate to Settings to verify language persistence
+      await page.getByTestId('sidebar-nav-settings').click();
+      await expect(page.getByTestId('settings-page')).toBeVisible();
+      
+      // Verify sidebar shows Russian text (not English)
+      // "Настройки" is Russian-only, English is "Settings"
+      await expect(page.getByTestId('sidebar-nav-settings')).toContainText('Настройки');
+    } finally {
+      await closeElectronApp(app);
+    }
+  });
+
+  test('can switch to Russian in Settings page', async ({ launchElectronApp }) => {
+    const app = await launchElectronApp({ skipSetup: true });
+    
+    try {
+      const page = await getStableWindow(app);
+      
+      await expect(page.getByTestId('main-layout')).toBeVisible();
+      
+      // Navigate to Settings (in English by default after skipSetup)
+      await page.getByTestId('sidebar-nav-settings').click();
+      await expect(page.getByTestId('settings-page')).toBeVisible();
+      
+      // Click Russian language button
+      const russianButton = page.locator('button', { hasText: 'Русский' });
+      await russianButton.click();
+      
+      // Verify sidebar switched to Russian
+      // "Настройки" is Russian-only, English is "Settings"
+      await expect(page.getByTestId('sidebar-nav-settings')).toContainText('Настройки');
+    } finally {
+      await closeElectronApp(app);
+    }
+  });
+});