[IMP] website: cannot deactivate language used by website

closes odoo/odoo#31520

---

backport of 8e2f9a4fe2
Initially a improvement, it is now backported in 12.0 to fix #34430

closes odoo/odoo#34474

Signed-off-by: Christophe Simonis <chs@odoo.com>

addons/website/models/__init__.py

@@ -13,3 +13,4 @@ from . import res_company
 from . import res_partner
 from . import res_users
 from . import res_config_settings
+from . import res_lang

addons/website/models/res_config_settings.py

@@ -18,7 +18,7 @@ class ResConfigSettings(models.TransientModel):
     website_domain = fields.Char('Website Domain', related='website_id.domain', readonly=False)
     website_country_group_ids = fields.Many2many(related='website_id.country_group_ids', readonly=False)
     website_company_id = fields.Many2one(related='website_id.company_id', string='Website Company', readonly=False)
-    language_ids = fields.Many2many(related='website_id.language_ids', relation='res.lang', readonly=False)
+    language_ids = fields.Many2many(related='website_id.language_ids', relation='res.lang', readonly=False, required=True)
     language_count = fields.Integer(string='Number of languages', compute='_compute_language_count', readonly=True)
     website_default_lang_id = fields.Many2one(
         string='Default language', related='website_id.default_lang_id', readonly=False,
@@ -106,7 +106,9 @@ class ResConfigSettings(models.TransientModel):
     def _onchange_language_ids(self):
         # If current default language is removed from language_ids
         # update the website_default_lang_id
-        if self.language_ids and self.website_default_lang_id not in self.language_ids:
+        if not self.language_ids:
+            self.website_default_lang_id = False
+        elif self.website_default_lang_id not in self.language_ids:
             self.website_default_lang_id = self.language_ids[0]
 
     @api.depends('language_ids')

addons/website/models/res_lang.py

@@ -0,0 +1,16 @@
+# -*- coding: utf-8 -*-
+# Part of Odoo. See LICENSE file for full copyright and licensing details.
+
+from odoo import api, models, _
+from odoo.exceptions import UserError
+
+
+class Lang(models.Model):
+    _inherit = "res.lang"
+
+    @api.multi
+    def write(self, vals):
+        if 'active' in vals and not vals['active']:
+            if self.env['website'].search([('language_ids', 'in', self._ids)]):
+                raise UserError(_("Cannot deactivate a language that is currently used on a website."))
+        return super(Lang, self).write(vals)