Wikimedia Bugzilla is closed!

I'm really sorry to open a bug with such a title. I guess I have mis-configured something, but after hours of researches this is the last action I see I can take.

I have MW 1.20.3 with MLEB 2013-2 and I'm not able to use the language selector to change the language: the language-selector is stuck. It's stuck to the browser preferred language as an anonymous and to English as a logged user.

You can check it by yourself (I have tested with FF and Chrome) at http://www.kiwix.org

My MLEB related conf:
                                                
$LANG_EXT = "$IP/extensions/";
$wgExtensionAssetsPath = "{$wgScriptPath}/extensions";
$ceAllowConfirmedEmail = true;

require_once( "$LANG_EXT/Babel/Babel.php" );
$wgBabelMainCategory = false;
$wgBabelCategoryNames = array(
                              '0' => 'User %code%-0',
                              '1' => 'User %code%-1',
                              '2' => 'User %code%-2',
                              '3' => 'User %code%-3',
                              '4' => 'User %code%-4',
                              '5' => 'User %code%-5',
                              'N' => 'User %code%-N',
                              );

require_once( "$LANG_EXT/cldr/cldr.php" );

require_once( "$LANG_EXT/CleanChanges/CleanChanges.php" );
$wgCCTrailerFilter = true;
$wgCCUserFilter = false;
$wgDefaultUserOptions['usenewrc'] = 1;

require_once( "$LANG_EXT/LocalisationUpdate/LocalisationUpdate.php" );
$wgLocalisationUpdateDirectory = "$IP/cache";

require_once( "$LANG_EXT/Translate/Translate.php" );
$wgGroupPermissions['user']['translate'] = true;
$wgGroupPermissions['user']['translate-messagereview'] = true;
$wgGroupPermissions['user']['translate-groupreview'] = true;
$wgGroupPermissions['user']['translate-import'] = true;
$wgGroupPermissions['sysop']['pagetranslation'] = true;
$wgGroupPermissions['sysop']['translate-manage'] = true;

$wgTranslateDocumentationLanguageCode = 'qqq';
$wgExtraLanguageNames['qqq'] = 'Message documentation';

require_once( "$LANG_EXT/UniversalLanguageSelector/UniversalLanguageSelector.php" );
$wgHiddenPrefs[] = 'language';

Last remark: to be more precise, there is one case where I can change the language, it's just after logging out, then I'm free to change the language; but as soon as I have loaded a page with the new configured language, then the language selector is again stuck.