[FIX] stock: dropshiping delivery slip in client's language

Steps to reprodue:
- Create a dropshipped product
- Sell the product to a client with a different language set
- Print the delivery slip

Bug:
delivery slip is currently being printed in the vendor's language

Fix:
Print the delivery slip in the client language when possible

opw-3193015

closes odoo/odoo#122706

X-original-commit: 832b4145
Signed-off-by: Adrien Widart (awt) <awt@odoo.com>
Signed-off-by: Walid Hanniche (waha) <waha@odoo.com>

addons/stock/models/stock_picking.py

@@ -1531,3 +1531,6 @@ class Picking(models.Model):
             body=message,
         )
         return True
+
+    def _get_report_lang(self):
+        return self.move_lines and self.move_lines[0].partner_id.lang or self.partner_id.lang or self.env.lang

addons/stock/report/report_deliveryslip.xml

@@ -3,7 +3,7 @@
     <template id="report_delivery_document">
         <t t-call="web.html_container">
             <t t-call="web.external_layout">
-                <t t-set="o" t-value="o.with_context(lang=o.partner_id.lang or o.env.lang)" />
+                <t t-set="o" t-value="o.with_context(lang=o._get_report_lang())" />
                 <t t-set="partner" t-value="o.partner_id or (o.move_lines and o.move_lines[0].partner_id) or False"/>
 
                 <t t-set="address">
@@ -272,7 +272,7 @@
 
     <template id="report_deliveryslip">
         <t t-foreach="docs" t-as="o">
-            <t t-call="stock.report_delivery_document" t-lang="o.partner_id.lang or o.env.lang"/>
+            <t t-call="stock.report_delivery_document" t-lang="o._get_report_lang()"/>
         </t>
     </template>
 </odoo>