Don't set default value for user language

issue4400
review12791002

trytond/res/user.py

@@ -301,7 +301,6 @@ class User(ModelSQL, ModelView):
         ModelData = pool.get('ir.model.data')
         Action = pool.get('ir.action')
         ConfigItem = pool.get('ir.module.module.config_wizard.item')
-        Config = pool.get('ir.configuration')
 
         res = {}
         if context_only:
@@ -314,7 +313,7 @@ class User(ModelSQL, ModelView):
                     if user.language:
                         res['language'] = user.language.code
                     else:
-                        res['language'] = Config.get_language()
+                        res['language'] = None
                 else:
                     res[field] = None
                     if getattr(user, field):