Internationalization (i18n) and Localization (l10n)

Example Code

<?php

// --- 1. Configuration and Language Data ---
// Define available languages and their respective translation files.
// In a real application, these might be loaded from a database or more complex file structure.
define('DEFAULT_LANGUAGE', 'en');
define('LANG_DIR', __DIR__ . '/lang/');

// Our simple translation data structure
$translations = [];

// --- 2. Language Detection and Loading ---

/
 * Detects the user's preferred language.
 * Priority: URL parameter > Session > Browser 'Accept-Language' > Default.
 *
 * @return string The detected language code (e.g., 'en', 'fr').
 */
function detectLanguage(): string {
    // 1. From URL parameter (e.g., ?lang=fr)
    if (isset($_GET['lang']) && !empty($_GET['lang'])) {
        $lang = strtolower($_GET['lang']);
        if (file_exists(LANG_DIR . $lang . '/messages.php')) {
            return $lang;
        }
    }

    // 2. From Session (if stored)
    // session_start(); // Uncomment if using sessions
    // if (isset($_SESSION['lang']) && file_exists(LANG_DIR . $_SESSION['lang'] . '/messages.php')) {
    //     return $_SESSION['lang'];
    // }

    // 3. From Browser's Accept-Language header
    if (isset($_SERVER['HTTP_ACCEPT_LANGUAGE'])) {
        $browser_langs = explode(',', $_SERVER['HTTP_ACCEPT_LANGUAGE']);
        foreach ($browser_langs as $browser_lang) {
            $lang_code = substr($browser_lang, 0, 2); // Get primary language part (e.g., 'en-US' -> 'en')
            if (file_exists(LANG_DIR . $lang_code . '/messages.php')) {
                // If using sessions, store it: $_SESSION['lang'] = $lang_code;
                return $lang_code;
            }
        }
    }

    // 4. Default language
    return DEFAULT_LANGUAGE;
}

/
 * Loads the translation messages for a given language.
 *
 * @param string $lang The language code to load.
 * @global array $translations The global array to store loaded translations.
 */
function loadTranslations(string $lang) {
    global $translations;
    $langFile = LANG_DIR . $lang . '/messages.php';

    if (file_exists($langFile)) {
        $translations = require $langFile;
    } else {
        // Fallback to default language if selected language file doesn't exist
        $defaultLangFile = LANG_DIR . DEFAULT_LANGUAGE . '/messages.php';
        if (file_exists($defaultLangFile)) {
            $translations = require $defaultLangFile;
        } else {
            $translations = []; // No translations available
        }
        error_log("Translation file not found for language: $lang. Falling back to default.");
    }
}

/
 * Translates a given key into the current language.
 * Supports basic string replacement for placeholders.
 *
 * @param string $key The key for the string to translate.
 * @param array $replacements An associative array of placeholders and their values.
 * @return string The translated string or the key itself if not found.
 */
function _t(string $key, array $replacements = []): string {
    global $translations;

    $translated_string = $translations[$key] ?? $key; // Fallback to key if not found

    foreach ($replacements as $placeholder => $value) {
        $translated_string = str_replace("{" . $placeholder . "}", $value, $translated_string);
    }

    return $translated_string;
}

// --- 3. Example Usage ---

// Set the current language
$currentLang = detectLanguage();
loadTranslations($currentLang);

// --- Create language files (if they don't exist) ---
// You need to create a 'lang' directory in the same location as this PHP file.
// Inside 'lang', create subdirectories 'en', 'fr', 'es'.
// Then, create 'messages.php' files inside each subdirectory with the content below.

// Example content for: lang/en/messages.php
/*
<?php
return [
    'hello_world' => 'Hello World!',
    'welcome_message' => 'Welcome to our website.',
    'messages_count' => 'You have {count} new messages.',
    'about_us' => 'About Us',
    'contact_us' => 'Contact Us',
    'choose_language' => 'Choose Language:',
    'english' => 'English',
    'french' => 'French',
    'spanish' => 'Spanish'
];
*/

// Example content for: lang/fr/messages.php
/*
<?php
return [
    'hello_world' => 'Bonjour le Monde!',
    'welcome_message' => 'Bienvenue sur notre site web.',
    'messages_count' => 'Vous avez {count} nouveaux messages.',
    'about_us' => 'À Propos de Nous',
    'contact_us' => 'Contactez-nous',
    'choose_language' => 'Choisir la langue :',
    'english' => 'Anglais',
    'french' => 'Français',
    'spanish' => 'Espagnol'
];
*/

// Example content for: lang/es/messages.php
/*
<?php
return [
    'hello_world' => '¡Hola Mundo!',
    'welcome_message' => 'Bienvenido a nuestro sitio web.',
    'messages_count' => 'Tienes {count} mensajes nuevos.',
    'about_us' => 'Sobre Nosotros',
    'contact_us' => 'Contáctenos',
    'choose_language' => 'Elija idioma:',
    'english' => 'Inglés',
    'french' => 'Francés',
    'spanish' => 'Español'
];
*/

?>
<!DOCTYPE html>
<html lang="<?php echo $currentLang; ?>">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title><?php echo _t('welcome_message'); ?></title>
    <style>
        body { font-family: Arial, sans-serif; margin: 20px; }
        .lang-switcher a { margin-right: 10px; text-decoration: none; }
    </style>
</head>
<body>
    <h1><?php echo _t('hello_world'); ?></h1>
    <p><?php echo _t('welcome_message'); ?></p>

    <?php $messageCount = 3; // Example variable ?>
    <p><?php echo _t('messages_count', ['count' => $messageCount]); ?></p>

    <nav>
        <ul>
            <li><a href="#"><?php echo _t('about_us'); ?></a></li>
            <li><a href="#"><?php echo _t('contact_us'); ?></a></li>
        </ul>
    </nav>

    <hr>

    <div class="lang-switcher">
        <p><?php echo _t('choose_language'); ?></p>
        <a href="?lang=en"><span><?php echo _t('english'); ?></span></a>
        <a href="?lang=fr"><span><?php echo _t('french'); ?></span></a>
        <a href="?lang=es"><span><?php echo _t('spanish'); ?></span></a>
    </div>

    <p>Current Language: <strong><?php echo $currentLang; ?></strong></p>

</body>
</html>