Impacted versions: 9, 10

Steps to reproduce:

1. Install mass_mailing.
2. Install an additional language (i.e. Spanish).
3. Log in as demo user.
4. Create a new partner, set its country to be "Spain".
4. Change demo user's lang to Spanish.
5. Create a new mass mailing.
5. Choose customer recipients.
5. Select those customers whose country is "España".
4. Design the email.
3. Send it.

Current behavior:
The demo user sees 1 record selected, the admin user sees 0 records. This happens because admin's lang is English and no countries are found if you search for "España" under that context.
Since the queue is sent under the admin user context, no mails are sent.
Demo user scratches his head (in case he ever notices no mails were sent).

Expected behavior:
Queue should be run under the same language as the one in the context when the user pressed the "send" button, to avoid losing records when some domain is applied over translated fields.

@Tecnativa
from datetime import datetime
import random
from odoo import api, fields, models, _
from odoo.exceptions import UserError
from odoo.tools.safe_eval import safe_eval
from odoo.tools.translate import html_translate
class MassMailingTag(models.Model):
    """Model of categories of mass mailing, i.e. marketing, newsletter, ... """
    _name = 'mail.mass_mailing.tag'
    _description = 'Mass Mailing Tag'
    _order = 'name'
    name = fields.Char(required=True, translate=True)
    color = fields.Integer(string='Color Index')
    _sql_constraints = [
            ('name_uniq', 'unique (name)', "Tag name already exists !"),
    ]
class MassMailingList(models.Model):
    """Model of a contact list. """
    _name = 'mail.mass_mailing.list'
    _order = 'name'
    _description = 'Mailing List'
    name = fields.Char(string='Mailing List', required=True)
    active = fields.Boolean(default=True)
    create_date = fields.Datetime(string='Creation Date')
    contact_nbr = fields.Integer(compute="_compute_contact_nbr", string='Number of Contacts')
    def _compute_contact_nbr(self):