erp5_xhtml_style: Do not redirect to external referer in Base_doLanguage

product/ERP5/bootstrap/erp5_xhtml_style/SkinTemplateItem/portal_skins/erp5_xhtml_style/Base_doLanguage.py

@@ -17,7 +17,8 @@ if website is not None and website.isStaticLanguageSelection():
     re.escape(root_website_url),
     '|'.join('/' + re.escape(x) for x in root_website.getAvailableLanguageList()))
   referer_url = context.REQUEST.HTTP_REFERER
-  if referer_url:
+  topmost_url_document = context.Base_getURLTopmostDocumentValue()
+  if referer_url and topmost_url_document.isURLAncestorOf(referer_url):
     if select_language == default_language:
       redirect_url = re.sub(website_url_pattern, root_website_url + r'\1', referer_url)
     else: