--- a/cubicweb/req.py	Wed Nov 02 15:59:39 2016 +0100
+++ b/cubicweb/req.py	Thu Nov 03 15:00:01 2016 +0100
@@ -76,6 +76,7 @@
         self.user = None
         self.local_perm_cache = {}
         self._ = text_type
+        self.lang = None
 
     def _set_user(self, orig_user):
         """set the user for this req_session_base
@@ -293,9 +294,13 @@
             path = kwargs.pop('_restpath')
         else:
             path = method
+        language = ''
+        if self.lang and self.vreg.config.get('language-mode') == 'url-prefix':
+            language = '%s/' % self.lang
         if not kwargs:
-            return u'%s%s' % (base_url, path)
-        return u'%s%s?%s' % (base_url, path, self.build_url_params(**kwargs))
+            return u'%s%s%s' % (base_url, language, path)
+        return u'%s%s%s?%s' % (base_url, language, path,
+                               self.build_url_params(**kwargs))
 
     def build_url_params(self, **kwargs):
         """return encoded params to incorporate them in a URL"""