For SEO and esthetical reasons, you may want the language parameter in a multilanguage content environment not as a simple GET parameter. Here is a hack that does that. It works against version 2.2.2 of Silverstripe - mileages may vary. The following recipe will create URL segments that look like /en/news or /de/neuigkeiten instead of /news/?lang=en or /news/?lang=de

First step is adding i18n support to the system as a whole. Change /mysite/_config.php, add the following lines and rebuild your database.

i18n::enable();
 
global $allowed_i18n;
$allowed_i18n = array('en' => "en_GB", 'es' => "es_ES", 'fr' => "fr_FR"); // these are the allowed language codes and the associated locales

Second: Load /sapphire/main.php and find the place that starts with

// Default director
Director::addRules(10, array(

Add before that the following code

$baseURL = dirname(dirname($_SERVER['SCRIPT_NAME']));
if(substr($url,0,strlen($baseURL)) == $baseURL) $url = substr($url,strlen($baseURL));
 
global $allowed_i18n;
if(sizeof($allowed_i18n) > 0) {
  $tmp_url = preg_replace( array( '/\/+/','/^\//', '/\/$/'),array('/','',''),$url);
  $tmp_urlParts = split('/+', $tmp_url);
  $lng = array_shift($tmp_urlParts);
  $bSetLng = false;
  if(isset($allowed_i18n[strtolower($lng)])) {
    i18n::set_locale($allowed_i18n[strtolower($lng)]); // SS locale.
    setlocale(LC_ALL, $allowed_i18n[strtolower($lng)]); // For l10n of dates, for example. The locale must be installed in the PHP environment.
    $url = "/".join('/', $tmp_urlParts);
    $_REQUEST['url']  = $url;
    $bSetLng = true;
  }
  // allow GET to overwrite the URL language selection
  if(isset($_GET['lang']) && in_array(strtolower($_GET['lang']), $allowed_i18n)) {
    $lng = $_GET['lang'];
    $bSetLng = true;
  }
  if($bSetLng) {
    $_GET['lang'] = $lng;
  }
  unset($lng, $bSetLng, $tmp_url, $tmp_urlParts);
}

This code basically splits up the url, looks for the first component and checks if this is a known language code from your _config.php change. If so it sets the GET parameter, reconstructs the URL and continues.

Third: In the same file, you find later on lines that read like that

// Get the request URL
$baseURL = dirname(dirname($_SERVER['SCRIPT_NAME']));
 
if(substr($url,0,strlen($baseURL)) == $baseURL) $url = substr($url,strlen($baseURL));

Delete these lines (or comment them out) to not to overwrite the changed (fixed) URL.

Fourth: Your /mysite/code/Page.php needs some code to know about current languages and translation names to help your templates. The minimum is

<?php
 
class Page extends SiteTree {
    static $db = array(
    );
    static $has_one = array(
    );
    function CurrentLang() {
        return (Translatable::current_lang()) ? Translatable::current_lang() : 'en';
    }
}
 
class Page_Controller extends ContentController {
    function init() {
        parent::init();
 
        Requirements::themedCSS("layout");
        Requirements::themedCSS("typography");
        Requirements::themedCSS("form");
    }
    function LanguageSwitcher() {
        if($this->URLSegment == "Security") return "";
        $langs = i18n::get_existing_content_languages();
        $data = new DataObjectSet();
        foreach(array_keys($langs) as $code) {
                if($code == Translatable::current_lang()) {
                        continue;
                }
                $page = Translatable::get_one_by_lang("SiteTree", $code, "`SiteTree`.ID = " . Controller::curr()->ID);
                $data->push(new ArrayData(array('name' => i18n::get_language_name($code, true),
                                                'link' => "/$code/" . $page->URLSegment,
                                                'code' => $code)));
        }
        return $data;
    }
}
?>

Fifth: Add a language switcher. Mine is called LanguageSwitcher.ss and lives in /themes/YOURS/templates/Includes/ and looks like that:

<link rel="stylesheet" href="/themes/sans/css/language.css" type="text/css" media="screen" />
<div id="languagecontainer">
  <ul id="language">
    <li><p>$CurrentLang</p></li>
    <% control LanguageSwitcher %>
      <li><a href="$link">$code</a></li>
    <% end_control %>
  </ul>
</div>

That way you can throw in a <% include LanguageSwitcher %> in your templates.

Caveats : From what I observed, you need to have distinct page names for all languages. /en/news and /fr/news will give you the news page from the default language. SS does not honor language/page combinations, it.seems