[FIX] sale_coupon: print report in customer lang

Before this commit, coupons were printed using the connected user language
instead of the customer language.

opw-1970448

closes odoo/enterprise#4142

Signed-off-by: Nicolas Martinelli (nim) <nim@odoo.com>

X-port/Cherry-pick of odoo/enterprise@5a4ce5a3bc

addons/sale_coupon/report/sale_coupon_report.xml

@@ -4,8 +4,8 @@
         <report
             id="report_coupon_code" 
             model="sale.coupon"
-            name="sale_coupon.report_coupon" 
-            file="sale_coupon.report_coupon"
+            name="sale_coupon.report_coupon_i18n"
+            file="sale_coupon.report_coupon_i18n"
             report_type="qweb-pdf"
             string="Coupon Code"/>
     </data>

addons/sale_coupon/report/sale_coupon_report_templates.xml

@@ -1,8 +1,6 @@
 <?xml version="1.0" encoding="utf-8"?>
 <odoo>
     <template id="report_coupon">
-        <t t-call="web.html_container">
-                <t t-foreach="docs" t-as="o">
                     <t t-call="web.internal_layout">
                     <div class="card">
                     <div class="card-body">
@@ -68,7 +66,14 @@
                     </div>
                 </div>
                 </div>
-                </t>
+        </t>
+    </template>
+
+    <template id="report_coupon_i18n">
+        <t t-call="web.html_container">
+            <t t-foreach="docs" t-as="o">
+                <t t-set="o" t-value="o.with_context(lang=o.partner_id.lang)"/>
+                <t t-call="sale_coupon.report_coupon" t-lang="o.partner_id.lang"/>
             </t>
         </t>
     </template>