diff -r 49bb5470d6ba trytond/trytond/modules/sale/sale.py
--- a/trytond/trytond/modules/sale/sale.py	Mon Nov 28 17:25:07 2016 +0100
+++ b/trytond/trytond/modules/sale/sale.py	Tue Dec 13 16:23:06 2016 +0100
@@ -1175,8 +1175,10 @@
         party_context = {}
         if self.sale and self.sale.party:
             party = self.sale.party
-            if party.lang:
-                party_context['language'] = party.lang.code
+        elif hasattr(self, 'party') and self.party:
+            party = self.party
+        if party and party.lang:
+            party_context['language'] = party.lang.code

         # Set taxes before unit_price to have taxes in context of sale price
         taxes = []