Index: ApiQuerySiteinfo.php
===================================================================
--- ApiQuerySiteinfo.php        (revision 50073)
+++ ApiQuerySiteinfo.php        (working copy)
@@ -120,6 +120,14 @@
                $data['rightscode'] = $GLOBALS['wgRightsCode'];
                $data['rights'] = $GLOBALS['wgRightsText'];
                $data['lang'] = $GLOBALS['wgLanguageCode'];
+               $fallbackLang = $wgContLang->getFallbackLanguageCode();
+               $fallbackLangArray = array();
+               while($fallbackLang){
+                       $fallbackLangArray[] = array('code' => $fallbackLang);
+                       $fallbackLang = Language::getFallbackFor($fallbackLang);
+               }
+               $data['fallback'] = $fallbackLangArray;
+               $this->getResult()->setIndexedTagName( $data['fallback'], 'lang' );
                if( $wgContLang->isRTL() )
                        $data['rtl'] = '';
                $data['fallback8bitEncoding'] = $wgLang->fallback8bitEncoding();