diff --git a/addons/mail/tests/common.py b/addons/mail/tests/common.py
index 3912398d5c3..675779e19e9 100644
--- a/addons/mail/tests/common.py
+++ b/addons/mail/tests/common.py
@@ -19,7 +19,7 @@ from odoo.addons.mail.models.mail_mail import MailMail
 from odoo.addons.mail.models.mail_message import Message
 from odoo.addons.mail.models.mail_notification import MailNotification
 from odoo.tests import common, new_test_user
-from odoo.tools import formataddr, pycompat
+from odoo.tools import formataddr, mute_logger, pycompat
 from odoo.tools.translate import code_translations
 
 mail_new_test_user = partial(new_test_user, context={'mail_create_nolog': True,
@@ -1102,9 +1102,9 @@ class MailCommon(common.TransactionCase, MailCase):
             * 'English Layout for' -> Spanish Layout para
           * model
             * description: English:    Lang Chatter Model (depends on test_record._name)
-                           translated: Spanish description
+                           translated: Spanish Model Description
           * module
-            * _('TestStuff') -> TestSpanishStuff (used as link button name in layout)
+            * _('NotificationButtonTitle') -> SpanishNotificationButtonTitle (used as link button name in layout)
             * _('View %s') -> SpanishView %s
           * template
             * body: English:    <p>EnglishBody for <t t-out="object.name"/></p> (depends on test_template.body)
@@ -1114,17 +1114,22 @@ class MailCommon(common.TransactionCase, MailCase):
         """
         # activate translations
         cls.env['res.lang']._activate_lang(lang_code)
-        cls.env.ref('base.module_base')._update_translations([lang_code])
+        with mute_logger("odoo.addons.base.models.ir_module", "odoo.tools.translate"):
+            cls.env.ref('base.module_base')._update_translations([lang_code])
+            cls.env.ref('base.module_mail')._update_translations([lang_code])
+            cls.env.ref('base.module_test_mail')._update_translations([lang_code])
+            code_translations.get_python_translations('mail', lang_code)
+            code_translations.get_python_translations('test_mail', lang_code)
 
         # Make sure Spanish translations have not been altered
         if test_record:
-            cls.env['ir.model']._get(test_record._name).with_context(lang=lang_code).name = 'Spanish description'
+            cls.env['ir.model']._get(test_record._name).with_context(lang=lang_code).name = 'Spanish Model Description'
 
         # Translate some code strings used in mailing
-        code_translations.python_translations[('test_mail', 'es_ES')] = {'TestStuff': 'TestSpanishStuff'}
-        cls.addClassCleanup(code_translations.python_translations.pop, ('test_mail', 'es_ES'))
-        code_translations.python_translations[('mail', 'es_ES')] = {'View %s': 'SpanishView %s'}
-        cls.addClassCleanup(code_translations.python_translations.pop, ('mail', 'es_ES'))
+        code_translations.python_translations[('test_mail', 'es_ES')]['NotificationButtonTitle'] = 'SpanishButtonTitle'
+        cls.addClassCleanup(code_translations.python_translations[('test_mail', 'es_ES')].pop, 'NotificationButtonTitle')
+        code_translations.python_translations[('mail', 'es_ES')]['View %s'] = 'SpanishView %s'
+        cls.addClassCleanup(code_translations.python_translations[('mail', 'es_ES')].pop, 'View %s')
 
         # Prepare some translated value for template if given
         if test_template:
diff --git a/addons/test_mail/models/test_mail_corner_case_models.py b/addons/test_mail/models/test_mail_corner_case_models.py
index e59aa431e40..31fd75ca27c 100644
--- a/addons/test_mail/models/test_mail_corner_case_models.py
+++ b/addons/test_mail/models/test_mail_corner_case_models.py
@@ -76,7 +76,7 @@ class MailTestLang(models.Model):
             group_options['has_button_access'] = True
             group_options['actions'] = [
                 {'url': self._notify_get_action_link('controller', controller='/test_mail/do_stuff', **local_msg_vals),
-                 'title': _('TestStuff')}
+                 'title': _('NotificationButtonTitle')}
             ]
         return groups
 
diff --git a/addons/test_mail/models/test_mail_models.py b/addons/test_mail/models/test_mail_models.py
index 8b3eec16f95..284e86956f6 100644
--- a/addons/test_mail/models/test_mail_models.py
+++ b/addons/test_mail/models/test_mail_models.py
@@ -225,7 +225,9 @@ class MailTestContainerMC(models.Model):
 
 class MailTestComposerMixin(models.Model):
     """ A simple invite-like wizard using the composer mixin, rendering on
-    itself. """
+    composer source test model. Purpose is to have a minimal composer which
+    runs on other records and check notably dynamic template support and
+    translations. """
     _description = 'Invite-like Wizard'
     _name = 'mail.test.composer.mixin'
     _inherit = ['mail.composer.mixin']
@@ -233,6 +235,25 @@ class MailTestComposerMixin(models.Model):
     name = fields.Char('Name')
     author_id = fields.Many2one('res.partner')
     description = fields.Html('Description', render_engine="qweb", render_options={"post_process": True}, sanitize=False)
+    source_ids = fields.Many2many('mail.test.composer.source', string='Invite source')
 
     def _compute_render_model(self):
-        self.render_model = self._name
+        self.render_model = 'mail.test.composer.source'
+
+
+class MailTestComposerSource(models.Model):
+    """ A simple model on which invites are sent. """
+    _description = 'Invite-like Wizard'
+    _name = 'mail.test.composer.source'
+    _inherit = ['mail.thread.blacklist']
+    _primary_email = 'email_from'
+
+    name = fields.Char('Name')
+    customer_id = fields.Many2one('res.partner', 'Main customer')
+    email_from = fields.Char(
+        'Email',
+        compute='_compute_email_from', readonly=False, store=True)
+
+    def _compute_email_from(self):
+        for source in self.filtered(lambda r: r.customer_id and not r.email_from):
+            source.email_from = source.customer_id.email_formatted
diff --git a/addons/test_mail/security/ir.model.access.csv b/addons/test_mail/security/ir.model.access.csv
index 0c6126ffb34..2fac058e400 100644
--- a/addons/test_mail/security/ir.model.access.csv
+++ b/addons/test_mail/security/ir.model.access.csv
@@ -19,6 +19,8 @@ access_mail_test_ticket_mc_portal,mail.test.ticket.mc.portal,model_mail_test_tic
 access_mail_test_ticket_mc_user,mail.test.ticket.mc.user,model_mail_test_ticket_mc,base.group_user,1,1,1,1
 access_mail_test_composer_mixin_all,mail.test.composer.mixin.all,model_mail_test_composer_mixin,,0,0,0,0
 access_mail_test_composer_mixin_user,mail.test.composer.mixin.user,model_mail_test_composer_mixin,base.group_user,1,1,1,1
+access_mail_test_composer_source_all,mail.test.composer.source.all,model_mail_test_composer_source,,1,0,0,0
+access_mail_test_composer_source_user,mail.test.composer.source.user,model_mail_test_composer_source,base.group_user,1,1,1,1
 access_mail_test_container_portal,mail.test.container_portal,model_mail_test_container,base.group_portal,1,0,0,0
 access_mail_test_container_user,mail.test.container.user,model_mail_test_container,base.group_user,1,1,1,1
 access_mail_test_container_mc_portal,mail.test.container.mc.portal,model_mail_test_container_mc,base.group_portal,1,0,0,0
diff --git a/addons/test_mail/tests/test_mail_composer_mixin.py b/addons/test_mail/tests/test_mail_composer_mixin.py
index 5b85c34ed5c..9591646b4a0 100644
--- a/addons/test_mail/tests/test_mail_composer_mixin.py
+++ b/addons/test_mail/tests/test_mail_composer_mixin.py
@@ -13,39 +13,101 @@ class TestMailComposerMixin(TestMailCommon, TestRecipients):
     def setUpClass(cls):
         super(TestMailComposerMixin, cls).setUpClass()
 
-        cls.mail_template = cls.env['mail.template'].create({
-            'subject': 'Subject for {{ object.name }}',
-            'body_html': '<p>Body for <t t-out="object.name"/></p>',
+        # ensure employee can create partners, necessary for templates
+        cls.user_employee.write({
+            'groups_id': [(4, cls.env.ref('base.group_partner_manager').id)],
         })
 
+        cls.mail_template = cls.env['mail.template'].create({
+            'body_html': '<p>EnglishBody for <t t-out="object.name"/></p>',
+            'model_id': cls.env['ir.model']._get('mail.test.composer.source').id,
+            'name': 'Test Template for mail.test.composer.source',
+            'lang': '{{ object.customer_id.lang }}',
+            'subject': 'EnglishSubject for {{ object.name }}',
+        })
+        cls.test_record = cls.env['mail.test.composer.source'].create({
+            'name': cls.partner_1.name,
+            'customer_id': cls.partner_1.id,
+        })
+
+        cls._activate_multi_lang(
+            layout_arch_db='<body><t t-out="message.body"/> English Layout for <t t-esc="model_description"/></body>',
+            lang_code='es_ES',
+            test_record=cls.test_record,
+            test_template=cls.mail_template,
+        )
+
     @users("employee")
     def test_content_sync(self):
-        record = self.env['mail.test.composer.mixin'].create({
+        """ Test updating template updates the dynamic fields accordingly. """
+        source = self.test_record.with_env(self.env)
+        composer = self.env['mail.test.composer.mixin'].create({
             'name': 'Invite',
             'template_id': self.mail_template.id,
+            'source_ids': [(4, source.id)],
         })
-        self.assertEqual(record.subject, self.mail_template.subject)
-        self.assertEqual(record.body, self.mail_template.body_html)
+        self.assertEqual(composer.body, self.mail_template.body_html)
+        self.assertEqual(composer.subject, self.mail_template.subject)
+        self.assertFalse(composer.lang, 'Fixme: lang is not propagated currently')
 
-        subject = record._render_field('subject', record.ids)[record.id]
-        self.assertEqual(subject, 'Subject for %s' % record.name)
-        body = record._render_field('body', record.ids)[record.id]
-        self.assertEqual(body, '<p>Body for %s</p>' % record.name)
+        subject = composer._render_field('subject', source.ids)[source.id]
+        self.assertEqual(subject, f'EnglishSubject for {source.name}')
+        body = composer._render_field('body', source.ids)[source.id]
+        self.assertEqual(body, f'<p>EnglishBody for {source.name}</p>')
 
     @users("employee")
-    def test_rendering(self):
-        record = self.env['mail.test.composer.mixin'].create({
-            'name': 'Invite',
-            'subject': 'Subject for {{ object.name }}',
-            'body': '<p>Content from <t t-out="user.name"/></p>',
+    def test_rendering_custom(self):
+        """ Test rendering with custom strings (not coming from template) """
+        source = self.test_record.with_env(self.env)
+        composer = self.env['mail.test.composer.mixin'].create({
             'description': '<p>Description for <t t-esc="object.name"/></p>',
+            'body': '<p>SpecificBody from <t t-out="user.name"/></p>',
+            'name': 'Invite',
+            'subject': 'SpecificSubject for {{ object.name }}',
         })
-        self.assertEqual(record.subject, 'Subject for {{ object.name }}')
-        self.assertEqual(record.body, '<p>Content from <t t-out="user.name"/></p>')
+        self.assertEqual(composer.body, '<p>SpecificBody from <t t-out="user.name"/></p>')
+        self.assertEqual(composer.subject, 'SpecificSubject for {{ object.name }}')
 
-        subject = record._render_field('subject', record.ids)[record.id]
-        self.assertEqual(subject, 'Subject for %s' % record.name)
-        body = record._render_field('body', record.ids)[record.id]
-        self.assertEqual(body, '<p>Content from %s</p>' % self.env.user.name)
-        description = record._render_field('description', record.ids)[record.id]
-        self.assertEqual(description, '<p>Description for Invite</p>')
+        subject = composer._render_field('subject', source.ids)[source.id]
+        self.assertEqual(subject, f'SpecificSubject for {source.name}')
+        body = composer._render_field('body', source.ids)[source.id]
+        self.assertEqual(body, f'<p>SpecificBody from {self.env.user.name}</p>')
+        description = composer._render_field('description', source.ids)[source.id]
+        self.assertEqual(description, f'<p>Description for {source.name}</p>')
+
+    @users("employee")
+    def test_rendering_lang(self):
+        """ Test rendering with language involved """
+        template = self.mail_template.with_env(self.env)
+        customer = self.partner_1.with_env(self.env)
+        customer.lang = 'es_ES'
+        source = self.test_record.with_env(self.env)
+        composer = self.env['mail.test.composer.mixin'].create({
+            'description': '<p>Description for <t t-esc="object.name"/></p>',
+            'lang': '{{ object.customer_id.lang }}',
+            'name': 'Invite',
+            'template_id': self.mail_template.id,
+            'source_ids': [(4, source.id)],
+        })
+        self.assertEqual(composer.body, template.body_html)
+        self.assertEqual(composer.subject, template.subject)
+        self.assertEqual(composer.lang, '{{ object.customer_id.lang }}')
+
+        # do not specifically ask for language computation
+        subject = composer._render_field('subject', source.ids, compute_lang=False)[source.id]
+        self.assertEqual(subject, f'EnglishSubject for {source.name}')
+        body = composer._render_field('body', source.ids, compute_lang=False)[source.id]
+        self.assertEqual(body, f'<p>EnglishBody for {source.name}</p>')
+        description = composer._render_field('description', source.ids)[source.id]
+        self.assertEqual(description, f'<p>Description for {source.name}</p>')
+
+        # ask for dynamic language computation
+        subject = composer._render_field('subject', source.ids, compute_lang=True)[source.id]
+        self.assertEqual(subject, f'EnglishSubject for {source.name}',
+                         'Fixme: translations are not done, as taking composer translations and not template one')
+        body = composer._render_field('body', source.ids, compute_lang=True)[source.id]
+        self.assertEqual(body, f'<p>EnglishBody for {source.name}</p>',
+                         'Fixme: translations are not done, as taking composer translations and not template one'
+        )
+        description = composer._render_field('description', source.ids)[source.id]
+        self.assertEqual(description, f'<p>Description for {source.name}</p>')
diff --git a/addons/test_mail/tests/test_mail_template.py b/addons/test_mail/tests/test_mail_template.py
index fb1bec1977e..678df090b6e 100644
--- a/addons/test_mail/tests/test_mail_template.py
+++ b/addons/test_mail/tests/test_mail_template.py
@@ -128,7 +128,7 @@ class TestMailTemplateLanguages(TestMailTemplateCommon):
         mail_id = test_template.send_mail(test_record.id, email_layout_xmlid='mail.test_layout')
         mail = self.env['mail.mail'].sudo().browse(mail_id)
         self.assertEqual(mail.body_html,
-                         '<body><p>SpanishBody for %s</p> Spanish Layout para Spanish description</body>' % self.test_record.name)
+                         '<body><p>SpanishBody for %s</p> Spanish Layout para Spanish Model Description</body>' % self.test_record.name)
         self.assertEqual(mail.subject, 'SpanishSubject for %s' % self.test_record.name)
 
     @mute_logger('odoo.addons.mail.models.mail_mail')
@@ -147,5 +147,5 @@ class TestMailTemplateLanguages(TestMailTemplateCommon):
         mail_id = test_template.send_mail(test_record.id, email_layout_xmlid='mail.test_layout')
         mail = self.env['mail.mail'].sudo().browse(mail_id)
         self.assertEqual(mail.body_html,
-                         '<body><p>SpanishBody for %s</p> Spanish Layout para Spanish description</body>' % self.test_record.name)
+                         '<body><p>SpanishBody for %s</p> Spanish Layout para Spanish Model Description</body>' % self.test_record.name)
         self.assertEqual(mail.subject, 'SpanishSubject for %s' % self.test_record.name)
diff --git a/addons/test_mail/tests/test_message_post.py b/addons/test_mail/tests/test_message_post.py
index 7341c9fd44a..b23052cc450 100644
--- a/addons/test_mail/tests/test_message_post.py
+++ b/addons/test_mail/tests/test_message_post.py
@@ -1210,7 +1210,49 @@ class TestMessagePostLang(TestMailCommon, TestRecipients):
 
     @users('employee')
     @mute_logger('odoo.addons.mail.models.mail_mail')
-    def test_composer_lang_template(self):
+    def test_composer_lang_template_comment(self):
+        test_record = self.test_records[0].with_user(self.env.user)
+        test_template = self.test_template.with_user(self.env.user)
+
+        with self.mock_mail_gateway():
+            test_record.message_post_with_template(
+                test_template.id,
+                composition_mode='comment',
+                email_layout_xmlid='mail.test_layout',
+                message_type='comment',
+                subtype_id=self.env.ref('mail.mt_comment').id,
+            )
+
+        record0_customer = self.env['res.partner'].search([('email_normalized', '=', 'test.record.1@test.customer.com')], limit=1)
+        self.assertTrue(record0_customer, 'Template usage should have created a contact based on record email')
+
+        customer_email = self._find_sent_mail_wemail(record0_customer.email_formatted)
+        self.assertTrue(customer_email)
+        body = customer_email['body']
+        # check content
+        self.assertIn(f'SpanishBody for {test_record.name}', body,
+                      'Body based on template should be translated')
+        # check subject
+        self.assertEqual(f'SpanishSubject for {test_record.name}', customer_email['subject'],
+                         'Subject based on template should be translated')
+        # check notification layout content
+        self.assertIn('Spanish Layout para', body, 'Layout content should be translated')
+        self.assertNotIn('English Layout for', body)
+        self.assertIn('Spanish Layout para Spanish Model Description', body, 'Model name should be translated')
+        # check notification layout strings
+        self.assertIn('View Lang Chatter Model', body,
+                      'Fixme: "View document" should be translated')
+        # self.assertIn('SpanishView Spanish Model Description', body,
+        #               '"View document" should be translated')
+        # self.assertNotIn(f'View {test_record._description}', body,
+        #                  '"View document" should be translated')
+        # self.assertIn('SpanishButtonTitle', body,
+        #               'Groups-based action names should be translated')
+        self.assertIn('NotificationButtonTitle', body, 'Fixme: Groups-based action names should be translated')
+
+    @users('employee')
+    @mute_logger('odoo.addons.mail.models.mail_mail')
+    def test_composer_lang_template_mass(self):
         test_records = self.test_records.with_user(self.env.user)
         test_template = self.test_template.with_user(self.env.user)
 
@@ -1231,11 +1273,15 @@ class TestMessagePostLang(TestMailCommon, TestRecipients):
             self.assertTrue(customer_email)
             body = customer_email['body']
             # check content
-            # self.assertIn('SpanishBody for %s' % record.name, body, 'Body based on template should be translated')
-            self.assertIn('EnglishBody for %s' % record.name, body, 'Fixme: this should be translated')
+            # self.assertIn(f'SpanishBody for {record.name}', body,
+            #               'Body based on template should be translated')
+            self.assertIn(f'EnglishBody for {record.name}', body,
+                          'Fixme: Body based on template should be translated')
             # check subject
-            # self.assertEqual('SpanishSubject for %s' % record.name, customer_email['subject'], 'Subject based on template should be translated')
-            self.assertEqual('EnglishSubject for %s' % record.name, customer_email['subject'], 'Fixme: this should be translated')
+            # self.assertEqual(f'SpanishSubject for {record.name}', customer_email['subject'],
+            #                  'Subject based on template should be translated')
+            self.assertEqual(f'EnglishSubject for {record.name}', customer_email['subject'],
+                             'Fixme: Subject based on template should be translated')
 
     @users('employee')
     @mute_logger('odoo.addons.mail.models.mail_mail')
@@ -1255,16 +1301,20 @@ class TestMessagePostLang(TestMailCommon, TestRecipients):
         customer_email = self._find_sent_mail_wemail(self.partner_2.email_formatted)
         self.assertTrue(customer_email)
         body = customer_email['body']
-        # check notification layout translation
-        self.assertIn('Spanish Layout para', body, 'Layout content should be translated')
-        self.assertNotIn('English Layout for', body)
-        self.assertIn('Spanish Layout para Spanish description', body, 'Model name should be translated')
-        self.assertIn('SpanishView Spanish description', body, '"View document" should be translated')
-        self.assertNotIn('View %s' % test_records[1]._description, body)
-        self.assertIn('TestSpanishStuff', body, 'Groups-based action names should be translated')
-        self.assertNotIn('TestStuff', body)
         # check content
-        self.assertIn('Hello', body, 'Body of posted message should be present')
+        self.assertIn('<p>Hello</p>', body, 'Body of posted message should be present')
+        # check notification layout content
+        self.assertIn('Spanish Layout para', body,
+                      'Layout content should be translated')
+        self.assertNotIn('English Layout for', body)
+        self.assertIn('Spanish Layout para Spanish Model Description', body,
+                      'Model name should be translated')
+        # check notification layout strings
+        self.assertIn('SpanishView Spanish Model Description', body,
+                      '"View document" should be translated')
+        self.assertNotIn(f'View {test_records[1]._description}', body)
+        self.assertIn('SpanishButtonTitle', body, 'Groups-based action names should be translated')
+        self.assertNotIn('NotificationButtonTitle', body)
 
     @users('employee')
     @mute_logger('odoo.addons.mail.models.mail_mail')
@@ -1288,15 +1338,23 @@ class TestMessagePostLang(TestMailCommon, TestRecipients):
             customer_email = self._find_sent_mail_wemail(customer.email_formatted)
             self.assertTrue(customer_email)
             body = customer_email['body']
-            # check notification layout translation
-            self.assertIn('Spanish Layout para', body, 'Layout content should be translated')
-            self.assertNotIn('English Layout for', body)
-            self.assertIn('Spanish Layout para Spanish description', body, 'Model name should be translated')
-            # self.assertIn('SpanishView Spanish description', body, '"View document" should be translated')
-            self.assertIn('View %s' % test_records[1]._description, body, 'Fixme: this should be translated')
-            # self.assertIn('TestSpanishStuff', body, 'Groups-based action names should be translated')
-            self.assertIn('TestStuff', body, 'Fixme: groups-based action names should be translated')
             # check content
-            self.assertIn('SpanishBody for %s' % record.name, body, 'Body based on template should be translated')
+            self.assertIn(f'SpanishBody for {record.name}', body,
+                          'Body based on template should be translated')
             # check subject
-            self.assertEqual('SpanishSubject for %s' % record.name, customer_email['subject'], 'Subject based on template should be translated')
+            self.assertEqual(f'SpanishSubject for {record.name}', customer_email['subject'],
+                             'Subject based on template should be translated')
+            # check notification layout translation
+            self.assertIn('Spanish Layout para', body,
+                          'Layout content should be translated')
+            self.assertNotIn('English Layout for', body)
+            self.assertIn('Spanish Layout para Spanish Model Description', body,
+                          'Model name should be translated')
+            # self.assertIn('SpanishView Spanish Model Description', body,
+            #               '"View document" should be translated')
+            self.assertIn(f'View {test_records[1]._description}', body,
+                          'Fixme: "View document" should be translated')
+            # self.assertIn('NotificationButtonTitle', body,
+            #               'Groups-based action names should be translated')
+            self.assertIn('NotificationButtonTitle', body,
+                          'Fixme: groups-based action names should be translated')