Add internationalization (i18n) support with English and Russian translations

Implemented localization system similar to the media-server project pattern:
- Created locale JSON files for English (en.json) and Russian (ru.json)
- Added complete translations for all UI elements, buttons, labels, and messages
- Implemented locale management system with browser locale detection
- Added language selector dropdown in header
- Applied data-i18n, data-i18n-title, and data-i18n-placeholder attributes
- Translations stored in localStorage and persist across sessions
- Automatic language detection from browser settings
- All dynamic content (displays, devices, modals) now uses translation function

Translations cover:
- Authentication (login/logout)
- Displays (layout visualization, cards, labels)
- Devices (management, status, actions)
- Settings modal (brightness, device configuration)
- Calibration modal (LED mapping, testing)
- Error messages and notifications
- Server status and version information

The implementation uses:
- Simple t(key, params) translation function with parameter substitution
- Async locale loading from /static/locales/{locale}.json
- updateAllText() to refresh all UI elements when language changes
- Fallback to English if translation file fails to load

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

server/src/wled_controller/static/app.js

@@ -2,8 +2,130 @@ const API_BASE = '/api/v1';
 let refreshInterval = null;
 let apiKey = null;
 
+// Locale management
+let currentLocale = 'en';
+let translations = {};
+const supportedLocales = {
+    'en': 'English',
+    'ru': 'Русский'
+};
+
+// Minimal inline fallback for critical UI elements
+const fallbackTranslations = {
+    'app.title': 'WLED Screen Controller',
+    'auth.placeholder': 'Enter your API key...',
+    'auth.button.login': 'Login'
+};
+
+// Translation function
+function t(key, params = {}) {
+    let text = translations[key] || fallbackTranslations[key] || key;
+
+    // Replace parameters like {name}, {value}, etc.
+    Object.keys(params).forEach(param => {
+        text = text.replace(new RegExp(`\\{${param}\\}`, 'g'), params[param]);
+    });
+
+    return text;
+}
+
+// Load translation file
+async function loadTranslations(locale) {
+    try {
+        const response = await fetch(`/static/locales/${locale}.json`);
+        if (!response.ok) {
+            throw new Error(`Failed to load ${locale}.json`);
+        }
+        return await response.json();
+    } catch (error) {
+        console.error(`Error loading translations for ${locale}:`, error);
+        // Fallback to English if loading fails
+        if (locale !== 'en') {
+            return await loadTranslations('en');
+        }
+        return {};
+    }
+}
+
+// Detect browser locale
+function detectBrowserLocale() {
+    const browserLang = navigator.language || navigator.languages?.[0] || 'en';
+    const langCode = browserLang.split('-')[0]; // 'en-US' -> 'en', 'ru-RU' -> 'ru'
+
+    // Only return if we support it
+    return supportedLocales[langCode] ? langCode : 'en';
+}
+
+// Initialize locale
+async function initLocale() {
+    const savedLocale = localStorage.getItem('locale') || detectBrowserLocale();
+    await setLocale(savedLocale);
+}
+
+// Set locale
+async function setLocale(locale) {
+    if (!supportedLocales[locale]) {
+        locale = 'en';
+    }
+
+    // Load translations for the locale
+    translations = await loadTranslations(locale);
+
+    currentLocale = locale;
+    document.documentElement.setAttribute('data-locale', locale);
+    document.documentElement.setAttribute('lang', locale);
+    localStorage.setItem('locale', locale);
+
+    // Update all text
+    updateAllText();
+
+    // Update locale select dropdown (if visible)
+    updateLocaleSelect();
+}
+
+// Change locale from dropdown
+function changeLocale() {
+    const select = document.getElementById('locale-select');
+    const newLocale = select.value;
+    if (newLocale && newLocale !== currentLocale) {
+        localStorage.setItem('locale', newLocale);
+        setLocale(newLocale);
+    }
+}
+
+// Update locale select dropdown
+function updateLocaleSelect() {
+    const select = document.getElementById('locale-select');
+    if (select) {
+        select.value = currentLocale;
+    }
+}
+
+// Update all text on page
+function updateAllText() {
+    // Update all elements with data-i18n attribute
+    document.querySelectorAll('[data-i18n]').forEach(el => {
+        const key = el.getAttribute('data-i18n');
+        el.textContent = t(key);
+    });
+
+    // Update all elements with data-i18n-placeholder attribute
+    document.querySelectorAll('[data-i18n-placeholder]').forEach(el => {
+        const key = el.getAttribute('data-i18n-placeholder');
+        el.placeholder = t(key);
+    });
+
+    // Update all elements with data-i18n-title attribute
+    document.querySelectorAll('[data-i18n-title]').forEach(el => {
+        const key = el.getAttribute('data-i18n-title');
+        el.title = t(key);
+    });
+}
+
 // Initialize app
-document.addEventListener('DOMContentLoaded', () => {
+document.addEventListener('DOMContentLoaded', async () => {
+    // Initialize locale first
+    await initLocale();
     // Load API key from localStorage
     apiKey = localStorage.getItem('wled_api_key');
 
@@ -97,13 +219,13 @@ async function loadServerInfo() {
         const response = await fetch('/health');
         const data = await response.json();
 
-        document.getElementById('server-version').textContent = `Version: ${data.version}`;
+        document.getElementById('version-number').textContent = data.version;
         document.getElementById('server-status').textContent = '●';
         document.getElementById('server-status').className = 'status-badge online';
     } catch (error) {
         console.error('Failed to load server info:', error);
         document.getElementById('server-status').className = 'status-badge offline';
-        showToast('Server offline', 'error');
+        showToast(t('server.offline'), 'error');
     }
 }
 
@@ -124,8 +246,8 @@ async function loadDisplays() {
         const container = document.getElementById('displays-list');
 
         if (!data.displays || data.displays.length === 0) {
-            container.innerHTML = '<div class="loading">No displays available</div>';
-            document.getElementById('display-layout-canvas').innerHTML = '<div class="loading">No displays available</div>';
+            container.innerHTML = `<div class="loading">${t('displays.none')}</div>`;
+            document.getElementById('display-layout-canvas').innerHTML = `<div class="loading">${t('displays.none')}</div>`;
             return;
         }
 
@@ -134,18 +256,18 @@ async function loadDisplays() {
             <div class="display-card">
                 <div class="display-header">
                     <div class="display-index">${display.name}</div>
-                    ${display.is_primary ? '<span class="badge badge-primary">Primary</span>' : '<span class="badge badge-secondary">Secondary</span>'}
+                    ${display.is_primary ? `<span class="badge badge-primary">${t('displays.badge.primary')}</span>` : `<span class="badge badge-secondary">${t('displays.badge.secondary')}</span>`}
                 </div>
                 <div class="info-row">
-                    <span class="info-label">Resolution:</span>
+                    <span class="info-label">${t('displays.resolution')}</span>
                     <span class="info-value">${display.width} × ${display.height}</span>
                 </div>
                 <div class="info-row">
-                    <span class="info-label">Position:</span>
+                    <span class="info-label">${t('displays.position')}</span>
                     <span class="info-value">(${display.x}, ${display.y})</span>
                 </div>
                 <div class="info-row">
-                    <span class="info-label">Display Index:</span>
+                    <span class="info-label">${t('displays.index')}</span>
                     <span class="info-value">${display.index}</span>
                 </div>
             </div>
@@ -156,9 +278,9 @@ async function loadDisplays() {
     } catch (error) {
         console.error('Failed to load displays:', error);
         document.getElementById('displays-list').innerHTML =
-            '<div class="loading">Failed to load displays</div>';
+            `<div class="loading">${t('displays.failed')}</div>`;
         document.getElementById('display-layout-canvas').innerHTML =
-            '<div class="loading">Failed to load layout</div>';
+            `<div class="loading">${t('displays.failed')}</div>`;
     }
 }
 
@@ -166,7 +288,7 @@ function renderDisplayLayout(displays) {
     const canvas = document.getElementById('display-layout-canvas');
 
     if (!displays || displays.length === 0) {
-        canvas.innerHTML = '<div class="loading">No displays to visualize</div>';
+        canvas.innerHTML = `<div class="loading">${t('displays.none')}</div>`;
         return;
     }
 

server/src/wled_controller/static/index.html

@@ -10,76 +10,80 @@
 <body>
     <div class="container">
         <header>
-            <h1>WLED Screen Controller</h1>
+            <h1 data-i18n="app.title">WLED Screen Controller</h1>
             <div class="server-info">
-                <span id="server-version">Version: Loading...</span>
+                <span id="server-version"><span data-i18n="app.version">Version:</span> <span id="version-number">Loading...</span></span>
                 <span id="server-status" class="status-badge">●</span>
-                <button class="theme-toggle" onclick="toggleTheme()" title="Toggle theme">
+                <button class="theme-toggle" onclick="toggleTheme()" data-i18n-title="theme.toggle" title="Toggle theme">
                     <span id="theme-icon">🌙</span>
                 </button>
+                <select id="locale-select" onchange="changeLocale()" data-i18n-title="locale.change" title="Change language" style="margin-left: 10px; padding: 6px 12px; border: 1px solid var(--border-color); border-radius: 4px; background: var(--bg-color); color: var(--text-color); font-size: 0.9rem; cursor: pointer;">
+                    <option value="en">English</option>
+                    <option value="ru">Русский</option>
+                </select>
                 <span id="auth-status" style="margin-left: 10px; display: none;">
-                    <span id="logged-in-user" style="color: #4CAF50; margin-right: 8px;">●</span>
+                    <span id="logged-in-user" style="color: #4CAF50; margin-right: 8px;" data-i18n="auth.authenticated">● Authenticated</span>
                 </span>
                 <button id="login-btn" class="btn btn-primary" onclick="showLogin()" style="display: none; padding: 6px 16px; font-size: 0.85rem; margin-left: 10px;">
-                    🔑 Login
+                    🔑 <span data-i18n="auth.login">Login</span>
                 </button>
                 <button id="logout-btn" class="btn btn-danger" onclick="logout()" style="display: none; padding: 6px 16px; font-size: 0.85rem; margin-left: 10px;">
-                    🚪 Logout
+                    🚪 <span data-i18n="auth.logout">Logout</span>
                 </button>
             </div>
         </header>
 
         <section class="displays-section">
-            <h2>Available Displays</h2>
+            <h2 data-i18n="displays.title">Available Displays</h2>
 
             <!-- Visual Layout Preview -->
             <div class="display-layout-preview">
-                <h3>Display Layout</h3>
+                <h3 data-i18n="displays.layout">Display Layout</h3>
                 <div id="display-layout-canvas" class="display-layout-canvas">
-                    <div class="loading">Loading layout...</div>
+                    <div class="loading" data-i18n="displays.loading">Loading layout...</div>
                 </div>
                 <div class="layout-legend">
-                    <span class="legend-item"><span class="legend-dot primary"></span> Primary Display</span>
-                    <span class="legend-item"><span class="legend-dot secondary"></span> Secondary Display</span>
+                    <span class="legend-item"><span class="legend-dot primary"></span> <span data-i18n="displays.legend.primary">Primary Display</span></span>
+                    <span class="legend-item"><span class="legend-dot secondary"></span> <span data-i18n="displays.legend.secondary">Secondary Display</span></span>
                 </div>
             </div>
 
             <!-- Display Cards -->
-            <h3 style="margin-top: 30px;">Display Information</h3>
+            <h3 style="margin-top: 30px;" data-i18n="displays.information">Display Information</h3>
             <div id="displays-list" class="displays-grid">
-                <div class="loading">Loading displays...</div>
+                <div class="loading" data-i18n="displays.loading">Loading displays...</div>
             </div>
         </section>
 
         <section class="devices-section">
-            <h2>WLED Devices</h2>
+            <h2 data-i18n="devices.title">WLED Devices</h2>
             <div id="devices-list" class="devices-grid">
-                <div class="loading">Loading devices...</div>
+                <div class="loading" data-i18n="devices.loading">Loading devices...</div>
             </div>
         </section>
 
         <section class="add-device-section">
-            <h2>Add New Device</h2>
+            <h2 data-i18n="devices.add">Add New Device</h2>
             <div class="info-banner" style="margin-bottom: 20px; padding: 12px; background: rgba(33, 150, 243, 0.1); border-left: 4px solid #2196F3; border-radius: 4px;">
-                <strong>📱 WLED Configuration:</strong> Configure your WLED device (effects, segments, color order, power limits, etc.) using the
-                <a href="https://kno.wled.ge/" target="_blank" rel="noopener" style="color: #2196F3; text-decoration: underline;">official WLED app</a>.
-                This controller sends pixel color data and controls brightness per device.
+                <strong><span data-i18n="devices.wled_config">📱 WLED Configuration:</span></strong> <span data-i18n="devices.wled_note">Configure your WLED device (effects, segments, color order, power limits, etc.) using the</span>
+                <a href="https://kno.wled.ge/" target="_blank" rel="noopener" style="color: #2196F3; text-decoration: underline;" data-i18n="devices.wled_link">official WLED app</a>.
+                <span data-i18n="devices.wled_note2">This controller sends pixel color data and controls brightness per device.</span>
             </div>
             <form id="add-device-form">
                 <div class="form-group">
-                    <label for="device-name">Device Name:</label>
-                    <input type="text" id="device-name" placeholder="Living Room TV" required>
+                    <label for="device-name" data-i18n="device.name">Device Name:</label>
+                    <input type="text" id="device-name" data-i18n-placeholder="device.name.placeholder" placeholder="Living Room TV" required>
                 </div>
                 <div class="form-group">
-                    <label for="device-url">WLED URL:</label>
-                    <input type="url" id="device-url" placeholder="http://192.168.1.100" required>
+                    <label for="device-url" data-i18n="device.url">WLED URL:</label>
+                    <input type="url" id="device-url" data-i18n-placeholder="device.url.placeholder" placeholder="http://192.168.1.100" required>
                 </div>
                 <div class="form-group">
-                    <label for="device-led-count">LED Count:</label>
+                    <label for="device-led-count" data-i18n="device.led_count">LED Count:</label>
                     <input type="number" id="device-led-count" value="150" min="1" required>
-                    <small class="input-hint">Number of LEDs configured in your WLED device</small>
+                    <small class="input-hint" data-i18n="device.led_count.hint">Number of LEDs configured in your WLED device</small>
                 </div>
-                <button type="submit" class="btn btn-primary">Add Device</button>
+                <button type="submit" class="btn btn-primary" data-i18n="device.button.add">Add Device</button>
             </form>
         </section>
     </div>
@@ -90,11 +94,11 @@
     <div id="calibration-modal" class="modal">
         <div class="modal-content" style="max-width: 700px;">
             <div class="modal-header">
-                <h2>📐 LED Calibration</h2>
+                <h2 data-i18n="calibration.title">📐 LED Calibration</h2>
             </div>
             <div class="modal-body">
                 <input type="hidden" id="calibration-device-id">
-                <p style="margin-bottom: 20px; color: var(--text-secondary);">
+                <p style="margin-bottom: 20px; color: var(--text-secondary);" data-i18n="calibration.description">
                     Configure how your LED strip is mapped to screen edges. Use test buttons to verify each edge lights up correctly.
                 </p>
 
@@ -102,22 +106,22 @@
                 <div style="margin-bottom: 25px;">
                     <div style="position: relative; width: 400px; height: 250px; margin: 0 auto; background: var(--card-bg); border: 2px solid var(--border-color); border-radius: 8px;">
                         <!-- Screen representation -->
-                        <div style="position: absolute; top: 50%; left: 50%; transform: translate(-50%, -50%); width: 300px; height: 180px; background: linear-gradient(135deg, #667eea 0%, #764ba2 100%); border-radius: 4px; display: flex; align-items: center; justify-content: center; color: white; font-size: 14px;">
+                        <div style="position: absolute; top: 50%; left: 50%; transform: translate(-50%, -50%); width: 300px; height: 180px; background: linear-gradient(135deg, #667eea 0%, #764ba2 100%); border-radius: 4px; display: flex; align-items: center; justify-content: center; color: white; font-size: 14px;" data-i18n="calibration.preview.screen">
                             Screen
                         </div>
 
                         <!-- Edge labels -->
                         <div style="position: absolute; top: 5px; left: 50%; transform: translateX(-50%); font-size: 12px; color: var(--text-secondary);">
-                            Top: <span id="preview-top-count">0</span> LEDs
+                            <span data-i18n="calibration.preview.top">Top:</span> <span id="preview-top-count">0</span> <span data-i18n="calibration.preview.leds">LEDs</span>
                         </div>
                         <div style="position: absolute; right: 5px; top: 50%; transform: translateY(-50%) rotate(90deg); font-size: 12px; color: var(--text-secondary); white-space: nowrap;">
-                            Right: <span id="preview-right-count">0</span> LEDs
+                            <span data-i18n="calibration.preview.right">Right:</span> <span id="preview-right-count">0</span> <span data-i18n="calibration.preview.leds">LEDs</span>
                         </div>
                         <div style="position: absolute; bottom: 5px; left: 50%; transform: translateX(-50%); font-size: 12px; color: var(--text-secondary);">
-                            Bottom: <span id="preview-bottom-count">0</span> LEDs
+                            <span data-i18n="calibration.preview.bottom">Bottom:</span> <span id="preview-bottom-count">0</span> <span data-i18n="calibration.preview.leds">LEDs</span>
                         </div>
                         <div style="position: absolute; left: 5px; top: 50%; transform: translateY(-50%) rotate(-90deg); font-size: 12px; color: var(--text-secondary); white-space: nowrap;">
-                            Left: <span id="preview-left-count">0</span> LEDs
+                            <span data-i18n="calibration.preview.left">Left:</span> <span id="preview-left-count">0</span> <span data-i18n="calibration.preview.leds">LEDs</span>
                         </div>
 
                         <!-- Starting position indicator -->
@@ -128,20 +132,20 @@
                 <!-- Layout Configuration -->
                 <div style="display: grid; grid-template-columns: 1fr 1fr; gap: 15px; margin-bottom: 20px;">
                     <div class="form-group">
-                        <label for="cal-start-position">Starting Position:</label>
+                        <label for="cal-start-position" data-i18n="calibration.start_position">Starting Position:</label>
                         <select id="cal-start-position" onchange="updateCalibrationPreview()">
-                            <option value="bottom_left">Bottom Left</option>
-                            <option value="bottom_right">Bottom Right</option>
-                            <option value="top_left">Top Left</option>
-                            <option value="top_right">Top Right</option>
+                            <option value="bottom_left" data-i18n="calibration.position.bottom_left">Bottom Left</option>
+                            <option value="bottom_right" data-i18n="calibration.position.bottom_right">Bottom Right</option>
+                            <option value="top_left" data-i18n="calibration.position.top_left">Top Left</option>
+                            <option value="top_right" data-i18n="calibration.position.top_right">Top Right</option>
                         </select>
                     </div>
 
                     <div class="form-group">
-                        <label for="cal-layout">Direction:</label>
+                        <label for="cal-layout" data-i18n="calibration.direction">Direction:</label>
                         <select id="cal-layout" onchange="updateCalibrationPreview()">
-                            <option value="clockwise">Clockwise</option>
-                            <option value="counterclockwise">Counterclockwise</option>
+                            <option value="clockwise" data-i18n="calibration.direction.clockwise">Clockwise</option>
+                            <option value="counterclockwise" data-i18n="calibration.direction.counterclockwise">Counterclockwise</option>
                         </select>
                     </div>
                 </div>
@@ -149,45 +153,45 @@
                 <!-- LED Counts per Edge -->
                 <div style="display: grid; grid-template-columns: 1fr 1fr; gap: 15px; margin-bottom: 20px;">
                     <div class="form-group">
-                        <label for="cal-top-leds">Top LEDs:</label>
+                        <label for="cal-top-leds" data-i18n="calibration.leds.top">Top LEDs:</label>
                         <input type="number" id="cal-top-leds" min="0" value="0" oninput="updateCalibrationPreview()">
                     </div>
 
                     <div class="form-group">
-                        <label for="cal-right-leds">Right LEDs:</label>
+                        <label for="cal-right-leds" data-i18n="calibration.leds.right">Right LEDs:</label>
                         <input type="number" id="cal-right-leds" min="0" value="0" oninput="updateCalibrationPreview()">
                     </div>
 
                     <div class="form-group">
-                        <label for="cal-bottom-leds">Bottom LEDs:</label>
+                        <label for="cal-bottom-leds" data-i18n="calibration.leds.bottom">Bottom LEDs:</label>
                         <input type="number" id="cal-bottom-leds" min="0" value="0" oninput="updateCalibrationPreview()">
                     </div>
 
                     <div class="form-group">
-                        <label for="cal-left-leds">Left LEDs:</label>
+                        <label for="cal-left-leds" data-i18n="calibration.leds.left">Left LEDs:</label>
                         <input type="number" id="cal-left-leds" min="0" value="0" oninput="updateCalibrationPreview()">
                     </div>
                 </div>
 
                 <div style="padding: 10px; background: rgba(255, 193, 7, 0.1); border-left: 4px solid #FFC107; border-radius: 4px; margin-bottom: 20px;">
-                    <strong>Total LEDs:</strong> <span id="cal-total-leds">0</span> / <span id="cal-device-led-count">0</span>
+                    <strong data-i18n="calibration.total">Total LEDs:</strong> <span id="cal-total-leds">0</span> / <span id="cal-device-led-count">0</span>
                 </div>
 
                 <!-- Test Buttons -->
                 <div style="margin-bottom: 15px;">
-                    <p style="font-weight: 600; margin-bottom: 10px;">Test Edges (lights up each edge):</p>
+                    <p style="font-weight: 600; margin-bottom: 10px;" data-i18n="calibration.test">Test Edges (lights up each edge):</p>
                     <div style="display: grid; grid-template-columns: repeat(4, 1fr); gap: 10px;">
                         <button class="btn btn-secondary" onclick="testCalibrationEdge('top')" style="font-size: 0.9rem; padding: 8px;">
-                            ⬆️ Top
+                            ⬆️ <span data-i18n="calibration.test.top">Top</span>
                         </button>
                         <button class="btn btn-secondary" onclick="testCalibrationEdge('right')" style="font-size: 0.9rem; padding: 8px;">
-                            ➡️ Right
+                            ➡️ <span data-i18n="calibration.test.right">Right</span>
                         </button>
                         <button class="btn btn-secondary" onclick="testCalibrationEdge('bottom')" style="font-size: 0.9rem; padding: 8px;">
-                            ⬇️ Bottom
+                            ⬇️ <span data-i18n="calibration.test.bottom">Bottom</span>
                         </button>
                         <button class="btn btn-secondary" onclick="testCalibrationEdge('left')" style="font-size: 0.9rem; padding: 8px;">
-                            ⬅️ Left
+                            ⬅️ <span data-i18n="calibration.test.left">Left</span>
                         </button>
                     </div>
                 </div>
@@ -195,8 +199,8 @@
                 <div id="calibration-error" class="error-message" style="display: none;"></div>
             </div>
             <div class="modal-footer">
-                <button class="btn btn-secondary" onclick="closeCalibrationModal()">Cancel</button>
-                <button class="btn btn-primary" onclick="saveCalibration()">Save Calibration</button>
+                <button class="btn btn-secondary" onclick="closeCalibrationModal()" data-i18n="calibration.button.cancel">Cancel</button>
+                <button class="btn btn-primary" onclick="saveCalibration()" data-i18n="calibration.button.save">Save Calibration</button>
             </div>
         </div>
     </div>
@@ -205,43 +209,43 @@
     <div id="device-settings-modal" class="modal">
         <div class="modal-content">
             <div class="modal-header">
-                <h2>⚙️ Device Settings</h2>
+                <h2 data-i18n="settings.title">⚙️ Device Settings</h2>
             </div>
             <div class="modal-body">
                 <form id="device-settings-form">
                     <input type="hidden" id="settings-device-id">
 
                     <div class="form-group">
-                        <label for="settings-device-name">Device Name:</label>
-                        <input type="text" id="settings-device-name" placeholder="Living Room TV" required>
+                        <label for="settings-device-name" data-i18n="device.name">Device Name:</label>
+                        <input type="text" id="settings-device-name" data-i18n-placeholder="device.name.placeholder" placeholder="Living Room TV" required>
                     </div>
 
                     <div class="form-group">
-                        <label for="settings-device-url">WLED URL:</label>
-                        <input type="url" id="settings-device-url" placeholder="http://192.168.1.100" required>
-                        <small class="input-hint">IP address or hostname of your WLED device</small>
+                        <label for="settings-device-url" data-i18n="device.url">WLED URL:</label>
+                        <input type="url" id="settings-device-url" data-i18n-placeholder="device.url.placeholder" placeholder="http://192.168.1.100" required>
+                        <small class="input-hint" data-i18n="settings.url.hint">IP address or hostname of your WLED device</small>
                     </div>
 
                     <div class="form-group">
-                        <label for="settings-device-led-count">LED Count:</label>
+                        <label for="settings-device-led-count" data-i18n="device.led_count">LED Count:</label>
                         <input type="number" id="settings-device-led-count" min="1" required>
-                        <small class="input-hint">Number of LEDs configured in your WLED device</small>
+                        <small class="input-hint" data-i18n="device.led_count.hint">Number of LEDs configured in your WLED device</small>
                     </div>
 
                     <div class="form-group">
-                        <label for="settings-device-brightness">Brightness: <span id="brightness-value">100%</span></label>
+                        <label for="settings-device-brightness"><span data-i18n="settings.brightness">Brightness:</span> <span id="brightness-value">100%</span></label>
                         <input type="range" id="settings-device-brightness" min="0" max="100" value="100"
                                oninput="document.getElementById('brightness-value').textContent = this.value + '%'"
                                style="width: 100%;">
-                        <small class="input-hint">Global brightness for this WLED device (0-100%)</small>
+                        <small class="input-hint" data-i18n="settings.brightness.hint">Global brightness for this WLED device (0-100%)</small>
                     </div>
 
                     <div id="settings-error" class="error-message" style="display: none;"></div>
                 </form>
             </div>
             <div class="modal-footer">
-                <button class="btn btn-secondary" onclick="closeDeviceSettingsModal()">Cancel</button>
-                <button class="btn btn-primary" onclick="saveDeviceSettings()">Save Changes</button>
+                <button class="btn btn-secondary" onclick="closeDeviceSettingsModal()" data-i18n="settings.button.cancel">Cancel</button>
+                <button class="btn btn-primary" onclick="saveDeviceSettings()" data-i18n="settings.button.save">Save Changes</button>
             </div>
         </div>
     </div>
@@ -250,18 +254,19 @@
     <div id="api-key-modal" class="modal">
         <div class="modal-content">
             <div class="modal-header">
-                <h2>🔑 Login to WLED Controller</h2>
+                <h2 data-i18n="auth.title">🔑 Login to WLED Controller</h2>
             </div>
             <div class="modal-body">
-                <p class="modal-description">
+                <p class="modal-description" data-i18n="auth.message">
                     Please enter your API key to authenticate and access the WLED Screen Controller.
                 </p>
                 <div class="form-group">
-                    <label for="api-key-input">API Key:</label>
+                    <label for="api-key-input" data-i18n="auth.label">API Key:</label>
                     <div class="password-input-wrapper">
                         <input
                             type="password"
                             id="api-key-input"
+                            data-i18n-placeholder="auth.placeholder"
                             placeholder="Enter your API key..."
                             autocomplete="off"
                         >
@@ -269,13 +274,13 @@
                             👁️
                         </button>
                     </div>
-                    <small class="input-hint">Your API key will be stored securely in your browser's local storage.</small>
+                    <small class="input-hint" data-i18n="auth.hint">Your API key will be stored securely in your browser's local storage.</small>
                 </div>
                 <div id="api-key-error" class="error-message" style="display: none;"></div>
             </div>
             <div class="modal-footer">
-                <button class="btn btn-secondary" onclick="closeApiKeyModal()" id="modal-cancel-btn">Cancel</button>
-                <button class="btn btn-primary" onclick="submitApiKey()">Login</button>
+                <button class="btn btn-secondary" onclick="closeApiKeyModal()" id="modal-cancel-btn" data-i18n="auth.button.cancel">Cancel</button>
+                <button class="btn btn-primary" onclick="submitApiKey()" data-i18n="auth.button.login">Login</button>
             </div>
         </div>
     </div>
@@ -329,20 +334,20 @@
         }
 
         function showLogin() {
-            showApiKeyModal('Enter your API key to login and access the controller.');
+            showApiKeyModal(t('auth.message'));
             document.getElementById('modal-cancel-btn').style.display = 'inline-block';
         }
 
         function logout() {
-            if (confirm('Are you sure you want to logout?')) {
+            if (confirm(t('auth.logout.confirm'))) {
                 localStorage.removeItem('wled_api_key');
                 apiKey = null;
                 updateAuthUI();
-                showToast('Logged out successfully', 'info');
+                showToast(t('auth.logout.success'), 'info');
 
                 // Clear the UI
-                document.getElementById('devices-list').innerHTML = '<div class="loading">Please login to view devices</div>';
-                document.getElementById('displays-list').innerHTML = '<div class="loading">Please login to view displays</div>';
+                document.getElementById('devices-list').innerHTML = `<div class="loading">${t('auth.please_login')} devices</div>`;
+                document.getElementById('displays-list').innerHTML = `<div class="loading">${t('auth.please_login')} displays</div>`;
             }
         }
 
@@ -395,7 +400,7 @@
             const key = input.value.trim();
 
             if (!key) {
-                error.textContent = 'Please enter an API key';
+                error.textContent = t('auth.error.required');
                 error.style.display = 'block';
                 return;
             }
@@ -406,7 +411,7 @@
             updateAuthUI();
 
             closeApiKeyModal();
-            showToast('Logged in successfully!', 'success');
+            showToast(t('auth.success'), 'success');
 
             // Reload data
             loadServerInfo();

server/src/wled_controller/static/locales/en.json

@@ -0,0 +1,111 @@
+{
+  "app.title": "WLED Screen Controller",
+  "app.version": "Version:",
+  "theme.toggle": "Toggle theme",
+  "locale.change": "Change language",
+  "auth.login": "Login",
+  "auth.logout": "Logout",
+  "auth.authenticated": "Authenticated",
+  "auth.title": "Login to WLED Controller",
+  "auth.message": "Please enter your API key to authenticate and access the WLED Screen Controller.",
+  "auth.label": "API Key:",
+  "auth.placeholder": "Enter your API key...",
+  "auth.hint": "Your API key will be stored securely in your browser's local storage.",
+  "auth.button.cancel": "Cancel",
+  "auth.button.login": "Login",
+  "auth.error.required": "Please enter an API key",
+  "auth.success": "Logged in successfully!",
+  "auth.logout.confirm": "Are you sure you want to logout?",
+  "auth.logout.success": "Logged out successfully",
+  "auth.please_login": "Please login to view",
+  "displays.title": "Available Displays",
+  "displays.layout": "Display Layout",
+  "displays.information": "Display Information",
+  "displays.legend.primary": "Primary Display",
+  "displays.legend.secondary": "Secondary Display",
+  "displays.badge.primary": "Primary",
+  "displays.badge.secondary": "Secondary",
+  "displays.resolution": "Resolution:",
+  "displays.position": "Position:",
+  "displays.index": "Display Index:",
+  "displays.loading": "Loading displays...",
+  "displays.none": "No displays available",
+  "displays.failed": "Failed to load displays",
+  "devices.title": "WLED Devices",
+  "devices.add": "Add New Device",
+  "devices.loading": "Loading devices...",
+  "devices.none": "No devices configured",
+  "devices.failed": "Failed to load devices",
+  "devices.wled_config": "WLED Configuration:",
+  "devices.wled_note": "Configure your WLED device (effects, segments, color order, power limits, etc.) using the",
+  "devices.wled_link": "official WLED app",
+  "devices.wled_note2": "This controller sends pixel color data and controls brightness per device.",
+  "device.name": "Device Name:",
+  "device.name.placeholder": "Living Room TV",
+  "device.url": "WLED URL:",
+  "device.url.placeholder": "http://192.168.1.100",
+  "device.led_count": "LED Count:",
+  "device.led_count.hint": "Number of LEDs configured in your WLED device",
+  "device.button.add": "Add Device",
+  "device.button.start": "Start",
+  "device.button.stop": "Stop",
+  "device.button.settings": "Settings",
+  "device.button.calibrate": "Calibrate",
+  "device.button.remove": "Remove",
+  "device.status.connected": "Connected",
+  "device.status.disconnected": "Disconnected",
+  "device.status.error": "Error",
+  "device.status.processing": "Processing",
+  "device.status.idle": "Idle",
+  "device.fps": "FPS:",
+  "device.display": "Display:",
+  "device.remove.confirm": "Are you sure you want to remove this device?",
+  "device.added": "Device added successfully",
+  "device.removed": "Device removed successfully",
+  "device.started": "Processing started",
+  "device.stopped": "Processing stopped",
+  "settings.title": "Device Settings",
+  "settings.brightness": "Brightness:",
+  "settings.brightness.hint": "Global brightness for this WLED device (0-100%)",
+  "settings.url.hint": "IP address or hostname of your WLED device",
+  "settings.button.cancel": "Cancel",
+  "settings.button.save": "Save Changes",
+  "settings.saved": "Settings saved successfully",
+  "settings.failed": "Failed to save settings",
+  "calibration.title": "LED Calibration",
+  "calibration.description": "Configure how your LED strip is mapped to screen edges. Use test buttons to verify each edge lights up correctly.",
+  "calibration.preview.screen": "Screen",
+  "calibration.preview.top": "Top:",
+  "calibration.preview.right": "Right:",
+  "calibration.preview.bottom": "Bottom:",
+  "calibration.preview.left": "Left:",
+  "calibration.preview.leds": "LEDs",
+  "calibration.start_position": "Starting Position:",
+  "calibration.position.bottom_left": "Bottom Left",
+  "calibration.position.bottom_right": "Bottom Right",
+  "calibration.position.top_left": "Top Left",
+  "calibration.position.top_right": "Top Right",
+  "calibration.direction": "Direction:",
+  "calibration.direction.clockwise": "Clockwise",
+  "calibration.direction.counterclockwise": "Counterclockwise",
+  "calibration.leds.top": "Top LEDs:",
+  "calibration.leds.right": "Right LEDs:",
+  "calibration.leds.bottom": "Bottom LEDs:",
+  "calibration.leds.left": "Left LEDs:",
+  "calibration.total": "Total LEDs:",
+  "calibration.test": "Test Edges (lights up each edge):",
+  "calibration.test.top": "Top",
+  "calibration.test.right": "Right",
+  "calibration.test.bottom": "Bottom",
+  "calibration.test.left": "Left",
+  "calibration.button.cancel": "Cancel",
+  "calibration.button.save": "Save Calibration",
+  "calibration.saved": "Calibration saved successfully",
+  "calibration.failed": "Failed to save calibration",
+  "calibration.testing": "Testing {edge} edge...",
+  "server.healthy": "Server online",
+  "server.offline": "Server offline",
+  "error.unauthorized": "Unauthorized - please login",
+  "error.network": "Network error",
+  "error.unknown": "An error occurred"
+}

server/src/wled_controller/static/locales/ru.json

@@ -0,0 +1,111 @@
+{
+  "app.title": "WLED Контроллер Экрана",
+  "app.version": "Версия:",
+  "theme.toggle": "Переключить тему",
+  "locale.change": "Изменить язык",
+  "auth.login": "Войти",
+  "auth.logout": "Выйти",
+  "auth.authenticated": "Авторизован",
+  "auth.title": "Вход в WLED Контроллер",
+  "auth.message": "Пожалуйста, введите ваш API ключ для аутентификации и доступа к WLED Контроллеру Экрана.",
+  "auth.label": "API Ключ:",
+  "auth.placeholder": "Введите ваш API ключ...",
+  "auth.hint": "Ваш API ключ будет безопасно сохранен в локальном хранилище браузера.",
+  "auth.button.cancel": "Отмена",
+  "auth.button.login": "Войти",
+  "auth.error.required": "Пожалуйста, введите API ключ",
+  "auth.success": "Вход выполнен успешно!",
+  "auth.logout.confirm": "Вы уверены, что хотите выйти?",
+  "auth.logout.success": "Выход выполнен успешно",
+  "auth.please_login": "Пожалуйста, войдите для просмотра",
+  "displays.title": "Доступные Дисплеи",
+  "displays.layout": "Расположение Дисплеев",
+  "displays.information": "Информация о Дисплеях",
+  "displays.legend.primary": "Основной Дисплей",
+  "displays.legend.secondary": "Вторичный Дисплей",
+  "displays.badge.primary": "Основной",
+  "displays.badge.secondary": "Вторичный",
+  "displays.resolution": "Разрешение:",
+  "displays.position": "Позиция:",
+  "displays.index": "Индекс Дисплея:",
+  "displays.loading": "Загрузка дисплеев...",
+  "displays.none": "Нет доступных дисплеев",
+  "displays.failed": "Не удалось загрузить дисплеи",
+  "devices.title": "WLED Устройства",
+  "devices.add": "Добавить Новое Устройство",
+  "devices.loading": "Загрузка устройств...",
+  "devices.none": "Устройства не настроены",
+  "devices.failed": "Не удалось загрузить устройства",
+  "devices.wled_config": "Конфигурация WLED:",
+  "devices.wled_note": "Настройте ваше WLED устройство (эффекты, сегменты, порядок цветов, ограничения питания и т.д.) используя",
+  "devices.wled_link": "официальное приложение WLED",
+  "devices.wled_note2": "Этот контроллер отправляет данные о цвете пикселей и управляет яркостью для каждого устройства.",
+  "device.name": "Имя Устройства:",
+  "device.name.placeholder": "ТВ в Гостиной",
+  "device.url": "WLED URL:",
+  "device.url.placeholder": "http://192.168.1.100",
+  "device.led_count": "Количество Светодиодов:",
+  "device.led_count.hint": "Количество светодиодов, настроенных в вашем WLED устройстве",
+  "device.button.add": "Добавить Устройство",
+  "device.button.start": "Запустить",
+  "device.button.stop": "Остановить",
+  "device.button.settings": "Настройки",
+  "device.button.calibrate": "Калибровка",
+  "device.button.remove": "Удалить",
+  "device.status.connected": "Подключено",
+  "device.status.disconnected": "Отключено",
+  "device.status.error": "Ошибка",
+  "device.status.processing": "Обработка",
+  "device.status.idle": "Ожидание",
+  "device.fps": "FPS:",
+  "device.display": "Дисплей:",
+  "device.remove.confirm": "Вы уверены, что хотите удалить это устройство?",
+  "device.added": "Устройство успешно добавлено",
+  "device.removed": "Устройство успешно удалено",
+  "device.started": "Обработка запущена",
+  "device.stopped": "Обработка остановлена",
+  "settings.title": "Настройки Устройства",
+  "settings.brightness": "Яркость:",
+  "settings.brightness.hint": "Общая яркость для этого WLED устройства (0-100%)",
+  "settings.url.hint": "IP адрес или имя хоста вашего WLED устройства",
+  "settings.button.cancel": "Отмена",
+  "settings.button.save": "Сохранить Изменения",
+  "settings.saved": "Настройки успешно сохранены",
+  "settings.failed": "Не удалось сохранить настройки",
+  "calibration.title": "Калибровка Светодиодов",
+  "calibration.description": "Настройте как ваша светодиодная лента сопоставляется с краями экрана. Используйте кнопки тестирования чтобы проверить что каждый край светится правильно.",
+  "calibration.preview.screen": "Экран",
+  "calibration.preview.top": "Сверху:",
+  "calibration.preview.right": "Справа:",
+  "calibration.preview.bottom": "Снизу:",
+  "calibration.preview.left": "Слева:",
+  "calibration.preview.leds": "Светодиодов",
+  "calibration.start_position": "Начальная Позиция:",
+  "calibration.position.bottom_left": "Нижний Левый",
+  "calibration.position.bottom_right": "Нижний Правый",
+  "calibration.position.top_left": "Верхний Левый",
+  "calibration.position.top_right": "Верхний Правый",
+  "calibration.direction": "Направление:",
+  "calibration.direction.clockwise": "По Часовой Стрелке",
+  "calibration.direction.counterclockwise": "Против Часовой Стрелки",
+  "calibration.leds.top": "Светодиодов Сверху:",
+  "calibration.leds.right": "Светодиодов Справа:",
+  "calibration.leds.bottom": "Светодиодов Снизу:",
+  "calibration.leds.left": "Светодиодов Слева:",
+  "calibration.total": "Всего Светодиодов:",
+  "calibration.test": "Тест Краев (подсвечивает каждый край):",
+  "calibration.test.top": "Сверху",
+  "calibration.test.right": "Справа",
+  "calibration.test.bottom": "Снизу",
+  "calibration.test.left": "Слева",
+  "calibration.button.cancel": "Отмена",
+  "calibration.button.save": "Сохранить Калибровку",
+  "calibration.saved": "Калибровка успешно сохранена",
+  "calibration.failed": "Не удалось сохранить калибровку",
+  "calibration.testing": "Тестирование {edge} края...",
+  "server.healthy": "Сервер онлайн",
+  "server.offline": "Сервер офлайн",
+  "error.unauthorized": "Не авторизован - пожалуйста, войдите",
+  "error.network": "Сетевая ошибка",
+  "error.unknown": "Произошла ошибка"
+}