Feature: Sistema multi-idioma con LibreTranslate

- Nuevo includes/i18n.php con funciones t() para traducción
- Selector de idioma en navbar y login
- Traducciones aplicadas a: dashboard, login, mensajes programados, crear mensaje, sistema
- Usa idiomas activados desde admin/languages.php
- Caché de traducciones incluido

includes/i18n.php

@@ -0,0 +1,131 @@
+<?php
+
+require_once __DIR__ . '/env_loader.php';
+require_once __DIR__ . '/../src/Translate.php';
+
+session_start();
+
+function getCurrentLanguage(): string
+{
+    if (isset($_SESSION['user_language'])) {
+        return $_SESSION['user_language'];
+    }
+    
+    if (isset($_COOKIE['user_language'])) {
+        $_SESSION['user_language'] = $_COOKIE['user_language'];
+        return $_COOKIE['user_language'];
+    }
+    
+    $defaultLang = 'es';
+    $_SESSION['user_language'] = $defaultLang;
+    return $defaultLang;
+}
+
+function setCurrentLanguage(string $langCode): void
+{
+    $_SESSION['user_language'] = $langCode;
+    setcookie('user_language', $langCode, [
+        'expires' => time() + (365 * 24 * 60 * 60),
+        'path' => '/',
+        'secure' => true,
+        'httponly' => true,
+        'samesite' => 'Strict'
+    ]);
+}
+
+function getActiveLanguages(): array
+{
+    static $languages = null;
+    
+    if ($languages !== null) {
+        return $languages;
+    }
+    
+    try {
+        $pdo = getDbConnection();
+        $stmt = $pdo->query("SELECT * FROM supported_languages WHERE is_active = 1 ORDER BY language_name");
+        $languages = $stmt->fetchAll();
+    } catch (Exception $e) {
+        $languages = [];
+    }
+    
+    return $languages;
+}
+
+function getBaseLanguage(): string
+{
+    return 'es';
+}
+
+function t(string $text, ?string $targetLang = null): string
+{
+    if (empty(trim($text))) {
+        return $text;
+    }
+    
+    $targetLang = $targetLang ?? getCurrentLanguage();
+    $baseLang = getBaseLanguage();
+    
+    if ($targetLang === $baseLang) {
+        return $text;
+    }
+    
+    static $translator = null;
+    static $cache = [];
+    
+    $cacheKey = md5($text . $targetLang);
+    
+    if (isset($cache[$cacheKey])) {
+        return $cache[$cacheKey];
+    }
+    
+    if ($translator === null) {
+        $translator = new \src\Translate();
+    }
+    
+    try {
+        $translated = $translator->translate($text, $baseLang, $targetLang);
+        
+        if ($translated !== null) {
+            $cache[$cacheKey] = $translated;
+            return $translated;
+        }
+    } catch (Exception $e) {
+        error_log("Translation error for '$text': " . $e->getMessage());
+    }
+    
+    return $text;
+}
+
+function ta(array $texts): array
+{
+    $result = [];
+    foreach ($texts as $key => $text) {
+        $result[$key] = t($text);
+    }
+    return $result;
+}
+
+function handleLanguageChange(): void
+{
+    if (isset($_GET['lang'])) {
+        $lang = $_GET['lang'];
+        $activeLanguages = getActiveLanguages();
+        $validLangs = array_column($activeLanguages, 'language_code');
+        
+        if (in_array($lang, $validLangs) || $lang === 'es') {
+            setCurrentLanguage($lang);
+        }
+        
+        $redirectUrl = strtok($_SERVER['REQUEST_URI'], '?');
+        $queryParams = $_GET;
+        unset($queryParams['lang']);
+        
+        if (!empty($queryParams)) {
+            $redirectUrl .= '?' . http_build_query($queryParams);
+        }
+        
+        header('Location: ' . $redirectUrl);
+        exit;
+    }
+}