diff --git a/tryton/translate.py b/tryton/translate.py
index 556dacdd21..1883f54671 100644
--- a/tryton/translate.py
+++ b/tryton/translate.py
@@ -180,7 +180,7 @@ def setlang(lang=None):
     else:
         try:
             if os.name == 'nt':
-                os.environ['LANG'] = None
+                os.environ['LANG'] = ''
             locale.setlocale(locale.LC_ALL, '')
         except:
             logging.getLogger('translate').warn(