[FIX] website_sale: set partner lang according to website lang

On ecommerce checkout, the language of the partner wasn't set according to the language in which he is visiting the website.
Therefore, its partner was set with the default language (English in most cases), and any emails sent to him were not translated in his own language (in the email templates, such as the quotation email he received on order confirmation)

addons/website_sale/controllers/main.py

@@ -510,7 +510,12 @@ class website_sale(http.Controller):
         orm_user = registry.get('res.users')
         order_obj = request.registry.get('sale.order')
 
-        billing_info = self.checkout_parse('billing', checkout, True)
+        partner_lang = request.lang if request.lang in [lang.code for lang in request.website.language_ids] else None
+
+        billing_info = {}
+        if partner_lang:
+            billing_info['lang'] = partner_lang
+        billing_info.update(self.checkout_parse('billing', checkout, True))
 
         # set partner_id
         partner_id = None
@@ -531,7 +536,10 @@ class website_sale(http.Controller):
 
         # create a new shipping partner
         if checkout.get('shipping_id') == -1:
-            shipping_info = self.checkout_parse('shipping', checkout, True)
+            shipping_info = {}
+            if partner_lang:
+                shipping_info['lang'] = partner_lang
+            shipping_info.update(self.checkout_parse('shipping', checkout, True))
             shipping_info['type'] = 'delivery'
             shipping_info['parent_id'] = partner_id
             checkout['shipping_id'] = orm_partner.create(cr, SUPERUSER_ID, shipping_info, context)