ZF: Bootstrap Process for I18n

application.ini

# Autoloader Namespaces
autoloaderNamespaces[] = "My_"

# Custom Resource Plugins
pluginPaths.My_Application_Resource = APPLICATION_PATH "/../lib/My/Application/Resource/"

# Front Controller Params
resources.frontController.params.locales[] = "en"
resources.frontController.params.locales[] = "ja"
resources.frontController.params.tldLocales.jp = "ja"

# Front Controller Plugins
resources.frontController.plugins.I18n = "My_Controller_Plugin_I18n"

# Locale
resources.locale.default = "en"

# Router/Routes
resources.router.locale.enabled = true
resources.router.routes.action_index.route = ":action/*"
resources.router.routes.action_index.defaults.controller = "index"
resources.router.routes.action_index.defaults.action = "index"

#resources.router.routes.action_index.type = "Zend_Controller_Router_Route_Regex"
#resources.router.routes.action_index.route = "(\w+)\/*"
#resources.router.routes.action_index.defaults.controller = "index"
#resources.router.routes.action_index.defaults.action = "index"
#resources.router.routes.action_index.map.1 = "action"

I18n.php

<?php
class My_Controller_Plugin_I18n extends Zend_Controller_Plugin_Abstract
{
    /**
    * Sets the application locale and translation based on the locale param, if
    * one is not provided it defaults to english
    *
    * @param Zend_Controller_Request_Abstract $request
    */
    public function routeShutdown(Zend_Controller_Request_Abstract $request)
    {
        $frontController = Zend_Controller_Front::getInstance();
        $params = $request->getParams();
        $registry = Zend_Registry::getInstance();

        // Steps setting the locale.
        // 1. Defaults to English (Done in config)
        // 2. TLD in host header
        // 3. Locale params specified in request
        $locale = $registry->get('Zend_Locale');

        // Check host header TLD.
        $tld = preg_replace('/^.*\./', '', $request->getHeader('Host'));

        // Provide a list of tld's and their corresponding default languages
        $tldLocales = $frontController->getParam('tldLocales');

        if (array_key_exists($tld, $tldLocales)) {
            // The TLD in the request matches one of our specified TLD -> Locales
            $locale->setLocale($tldLocales[$tld]);
        } else if (isset($params['locale'])) {
            // There is a locale specified in the request params.
            $locale->setLocale($params['locale']);
        }

        // Now that our locale is set, let's check which language has been selected
        // and try to load a translation file for it. If the language is the default,
        // then we do not need to load a translation.
        $language = $locale->getLanguage();
        if ($language !== $locale->getDefault()) {
            $i18nFile = APPLICATION_PATH . '/data/i18n/source-' . $language . '.mo';
            try {
                $translate =
                    new Zend_Translate('gettext', $i18nFile, $locale, array('disableNotices' => true));

                Zend_Registry::set('Zend_Translate', $translate);
                Zend_Form::setDefaultTranslator($translate);
            } catch (Zend_Translate_Exception $e) {
                // Since there was an error when trying to load the translation catalog,
                // let's not load a translation object which essentially defaults to
                // locale default.
            }
        }

        // Now that we have our locale setup, let's check to see if we are loading
        // a language that is not the default, and update our base URL on the front
        // controller to the specified language.
        $defaultLanguage = array_keys($locale->getDefault());
        $defaultLanguage = $defaultLanguage[0];

        $path = '/' . ltrim($request->getPathInfo(), '/\\');

        // If the language is in the path, then we will want to set the baseUrl
        // to the specified language.
        if (preg_match('/^\/' . $language . '\/?/', $path)) {
            $viewRenderer =
                Zend_Controller_Action_HelperBroker::getStaticHelper('viewRenderer');
            $view = $viewRenderer->view;

            $baseUrl = $frontController->getBaseUrl() . '/' . $language;
            $frontController->setBaseUrl($baseUrl);
            $view->getHelper('BaseUrl')->setBaseUrl($baseUrl);
        }

        setcookie('Zend_Locale', $language, null, '/', $request->getHttpHost());
    }
}

LocaleSwitcher.php

<?php
class Default_View_Helper_LocaleSwitcher extends Zend_View_Helper_Abstract
{
    public function localeSwitcher()
    {
        $output = array();
        $frontController = Zend_Controller_Front::getInstance();

        $locales = $frontController->getParam('locales');
        $request = $frontController->getRequest();
        $baseUrl = $request->getBaseUrl();
        $path = '/' . trim($request->getPathInfo(), '/\\');

        if (count($locales) > 0) {
            $locale = Zend_Registry::get('Zend_Locale');
            $localeLanguage = $locale->getLanguage();
            $defaultLocaleLanguage = array_keys($locale->getDefault());
            $defaultLocaleLanguage = $defaultLocaleLanguage[0];

            array_push($output, '<ul id="locale_switcher">');

            foreach ($locales as $language) {
                $imageSrc  = 'img/i18n_';
                $imageSrc .= $language . '_' . ($localeLanguage == $language ? 'on' : 'off');
                $imageSrc .= '.gif';

                $urlLanguage = $defaultLocaleLanguage == $language
                    ? ''
                    : '/' . $language;

                if (strlen($baseUrl) === 0) {
                    $localeUrl = $urlLanguage . $path;
                } else {
                    $localeUrl = preg_replace('/^' . preg_quote($baseUrl, '/') . '\/?/',
                        $urlLanguage . '/', $path);
                }

                array_push($output, '<li>');
                array_push($output, '<a href="' . $localeUrl . '">');
                array_push($output, '<img src="' . $this->view->assetUrl($imageSrc) . '" alt="' . $language . '" />');
                array_push($output, '</a>');
                array_push($output, '</li>');
            }

            array_push($output, '</ul>');
        }

        return join('', $output);
    }
}

Router.php

<?php
class My_Application_Resource_Router extends Zend_Application_Resource_Router
{
    public $_explicitType = 'router';

    protected $_front;
    protected $_locale;

    /**
     * Retrieve router object
     *
     * @return Zend_Controller_Router_Rewrite
     */
    public function getRouter()
    {
        $options = $this->getOptions();

        if (!isset($options['locale']['enabled']) ||
            !$options['locale']['enabled']) {
            return parent::getRouter();
        }

        $bootstrap = $this->getBootstrap();

        if (!$this->_front) {
            $bootstrap->bootstrap('FrontController');
            $this->_front = $bootstrap->getContainer()->frontcontroller;
        }

        if (!$this->_locale) {
            $bootstrap->bootstrap('Locale');
            $this->_locale = $bootstrap->getContainer()->locale;
        }

        $defaultLocale = array_keys($this->_locale->getDefault());
        $defaultLocale = $defaultLocale[0];

        $locales = $this->_front->getParam('locales');
        $requiredLocalesRegex = '^(' . join('|', $locales) . ')$';

        $routes = $options['routes'];
        foreach ($routes as $key => $value) {
            // First let's add the default locale to this routes defaults.
            $defaults = isset($value['defaults'])
                ? $value['defaults']
                : array();

            // Always default all routes to the Zend_Locale default
            $value['defaults'] = array_merge(array( 'locale' => $defaultLocale ), $defaults);

            $routes[$key] = $value;

            // Get our route and make sure to remove the first forward slash
            // since it's not needed.
            $routeString = $value['route'];
            $routeString = ltrim($routeString, '/\\');

            // Modify our normal route to have the locale parameter.
            if (!isset($value['type']) ||
                $value['type'] === 'Zend_Controller_Router_Route') {
                $value['route'] = ':locale/' . $routeString;

                $value['reqs']['locale'] = $requiredLocalesRegex;

                $routes['locale_' . $key] = $value;
            } else if ($value['type'] === 'Zend_Controller_Router_Route_Regex') {
                $value['route'] = '(' . join('|', $locales) . ')\/' . $routeString;

                // Since we added the local regex match, we need to bump the existing
                // match numbers plus one.
                $map = isset($value['map']) ? $value['map'] : array();
                foreach ($map as $index => $word) {
                    unset($map[$index++]);
                    $map[$index] = $word;
                }

                // Add our locale map
                $map[1] = 'locale';
                ksort($map);

                $value['map'] = $map;

                $routes['locale_' . $key] = $value;
            } else if ($value['type'] === 'Zend_Controller_Router_Route_Static') {
                foreach ($locales as $locale) {
                    $value['route'] = $locale . '/' . $routeString;
                    $value['defaults']['locale'] = $locale;
                    $routes['locale_' . $locale . '_' . $key] = $value;
                }
            }
        }

        $options['routes'] = $routes;
        $this->setOptions($options);

        return parent::getRouter();
    }
}

hey @jgornick , great snippet/example , one note tho, for me the .ini comments are starting with semicolons (;), hashes (#) are not allowed.