[FIX] mass_mailing: domain translation

As Admin:
- Set up 2 languages for the installation, e.g. English and French
- Admin language is English, Demo language is French
- Create a `res.partner.category` named 'Test English'
- Assign the category to a newly created partner
- Create a French translation for 'Test English', e.g. 'Test Francais'

As Demo:
- Create a Mass Mailing
- Select a custom domain: ('category_id', '=', 'Test Francais') => it
  should match one partner
- Save and validate

Now either:
- manually run the scheduled action "Process Mass Mailing Queue" as
  Admin
- wait for the cron to process the mass mailing

No mail will be sent since the domain will be evaluated in the Admin
language, i.e. English. Indeed, the domain
`('category_id', '=', 'Test Francais')` does not match any record in
English.

The solution/workaround is to use the language of the last user who wrote
ont the mass mailing.

Closes #20906, Closes #15467, Closes #15445

opw-778922

addons/mass_mailing/models/mass_mailing.py

@@ -611,6 +611,8 @@ class MassMailing(models.Model):
     def _process_mass_mailing_queue(self):
         mass_mailings = self.search([('state', 'in', ('in_queue', 'sending')), '|', ('schedule_date', '<', fields.Datetime.now()), ('schedule_date', '=', False)])
         for mass_mailing in mass_mailings:
+            user = mass_mailing.write_uid or self.env.user
+            mass_mailing = mass_mailing.with_context(**user.sudo(user=user).context_get())
             if len(mass_mailing.get_remaining_recipients()) > 0:
                 mass_mailing.state = 'sending'
                 mass_mailing.send_mail()