Implement internationalization (i18n) system for LoRA Manager

- Added i18n support with automatic language detection based on browser settings.
- Implemented translations for English (en) and Simplified Chinese (zh-CN).
- Created utility functions for text replacement in HTML templates and JavaScript.
- Developed a comprehensive translation key structure for various application components.
- Added formatting functions for numbers, dates, and file sizes according to locale.
- Included RTL language support and dynamic updates for DOM elements.
- Created tests to verify the functionality of the i18n system.

static/js/test/i18nTest.js

@@ -0,0 +1,123 @@
+/**
+ * i18n System Test
+ * Simple test to verify internationalization functionality
+ */
+
+import { i18n } from '../i18n/index.js';
+import { initializePageI18n, t, formatFileSize, formatDate, formatNumber } from '../utils/i18nHelpers.js';
+
+// Mock DOM elements for testing
+function createMockDOM() {
+    // Create a test container
+    const container = document.createElement('div');
+    container.innerHTML = `
+        <div data-i18n="header.appTitle">LoRA Manager</div>
+        <input data-i18n="header.search.placeholder" data-i18n-target="placeholder" placeholder="Search..." />
+        <button data-i18n="common.actions.save">Save</button>
+        <span data-i18n="loras.bulkOperations.selected" data-i18n-params='{"count": 5}'>5 selected</span>
+    `;
+    document.body.appendChild(container);
+    return container;
+}
+
+// Test basic translation functionality
+function testBasicTranslation() {
+    console.log('=== Testing Basic Translation ===');
+    
+    // Test simple translation
+    const saveText = t('common.actions.save');
+    console.log(`Save button text: ${saveText}`);
+    
+    // Test translation with parameters
+    const selectedText = t('loras.bulkOperations.selected', { count: 3 });
+    console.log(`Selection text: ${selectedText}`);
+    
+    // Test non-existent key (should return the key itself)
+    const missingKey = t('non.existent.key');
+    console.log(`Missing key: ${missingKey}`);
+}
+
+// Test DOM translation
+function testDOMTranslation() {
+    console.log('=== Testing DOM Translation ===');
+    
+    const container = createMockDOM();
+    
+    // Apply translations
+    initializePageI18n();
+    
+    // Check if translations were applied
+    const titleElement = container.querySelector('[data-i18n="header.appTitle"]');
+    const inputElement = container.querySelector('input[data-i18n="header.search.placeholder"]');
+    const buttonElement = container.querySelector('[data-i18n="common.actions.save"]');
+    
+    console.log(`Title: ${titleElement.textContent}`);
+    console.log(`Input placeholder: ${inputElement.placeholder}`);
+    console.log(`Button: ${buttonElement.textContent}`);
+    
+    // Clean up
+    document.body.removeChild(container);
+}
+
+// Test formatting functions
+function testFormatting() {
+    console.log('=== Testing Formatting Functions ===');
+    
+    // Test file size formatting
+    const sizes = [0, 1024, 1048576, 1073741824];
+    sizes.forEach(size => {
+        const formatted = formatFileSize(size);
+        console.log(`${size} bytes = ${formatted}`);
+    });
+    
+    // Test date formatting
+    const date = new Date('2024-01-15T10:30:00');
+    const formattedDate = formatDate(date, { 
+        year: 'numeric', 
+        month: 'long', 
+        day: 'numeric' 
+    });
+    console.log(`Date: ${formattedDate}`);
+    
+    // Test number formatting
+    const number = 1234.567;
+    const formattedNumber = formatNumber(number, { 
+        minimumFractionDigits: 2,
+        maximumFractionDigits: 2
+    });
+    console.log(`Number: ${formattedNumber}`);
+}
+
+// Test language detection
+function testLanguageDetection() {
+    console.log('=== Testing Language Detection ===');
+    console.log(`Detected language: ${i18n.getCurrentLocale()}`);
+    console.log(`Is RTL: ${i18n.isRTL()}`);
+    console.log(`Browser language: ${navigator.language}`);
+}
+
+// Run all tests
+function runTests() {
+    console.log('Starting i18n System Tests...');
+    console.log('=====================================');
+    
+    testLanguageDetection();
+    testBasicTranslation();
+    testFormatting();
+    
+    // Only test DOM if we're in a browser environment
+    if (typeof document !== 'undefined') {
+        testDOMTranslation();
+    }
+    
+    console.log('=====================================');
+    console.log('i18n System Tests Completed!');
+}
+
+// Export for manual testing
+export { runTests };
+
+// Auto-run tests if this module is loaded directly
+if (typeof window !== 'undefined' && window.location.search.includes('test=i18n')) {
+    document.addEventListener('DOMContentLoaded', runTests);
+}