fix(notifications): translate notification emails and messages into recipient user locale (#11408) (#12944)

* fix(notifications): translate notification emails and messages into recipient user locale (#11408)

* add a codespell ignore for the translated assertation

---------

Co-authored-by: Matthias Mair <code@mjmair.com>

src/backend/InvenTree/common/notifications.py

@@ -84,6 +84,39 @@ class InvenTreeNotificationBodies:
     )
 
 
+def get_user_language(user) -> str:
+    """Return the preferred language code for a user, or default system language."""
+    from django.conf import settings
+
+    if not user:
+        return getattr(settings, 'LANGUAGE_CODE', 'en-us')
+
+    # 1. Try user.profile.language (UserProfile model relation)
+    if profile := getattr(user, 'profile', None):
+        if lang := getattr(profile, 'language', None):
+            return lang
+
+    # 2. Try user.user_profile.language (alias if present)
+    if profile := getattr(user, 'user_profile', None):
+        if lang := getattr(profile, 'language', None):
+            return lang
+
+    # 3. Try InvenTreeUserSetting for 'LANGUAGE'
+    try:
+        from common.models import InvenTreeUserSetting
+
+        lang = InvenTreeUserSetting.get_setting(
+            'LANGUAGE', user=user, backup_value=None
+        )
+        if lang:
+            return lang
+    except Exception:
+        pass
+
+    # 4. Fallback to settings.LANGUAGE_CODE
+    return getattr(settings, 'LANGUAGE_CODE', 'en-us')
+
+
 def trigger_notification(obj: Model, category: str = '', obj_ref: str = 'pk', **kwargs):
     """Send out a notification.
 

src/backend/InvenTree/common/test_notifications.py

@@ -0,0 +1,204 @@
+"""Unit tests for notification locale translations (Issue #11408)."""
+
+from unittest.mock import patch
+
+from django.conf import settings
+from django.contrib.auth import get_user_model
+from django.utils.translation import gettext_lazy as _
+
+from common.models import InvenTreeUserSetting, NotificationMessage
+from common.notifications import get_user_language
+from InvenTree.unit_test import InvenTreeTestCase
+from plugin.builtin.integration.core_notifications import (
+    InvenTreeEmailNotifications,
+    InvenTreeUINotifications,
+)
+from plugin.models import PluginConfig
+
+User = get_user_model()
+
+
+class NotificationLocaleTest(InvenTreeTestCase):
+    """Unit tests for notification locale translations."""
+
+    @classmethod
+    def setUpTestData(cls):
+        """Set up test data for notification locale testing."""
+        super().setUpTestData()
+
+        # Ensure the email plugin config exists and is active
+        PluginConfig.objects.get_or_create(
+            key='inventree-email-notification',
+            defaults={'name': 'InvenTreeEmailNotifications', 'active': True},
+        )
+
+        # Create English user
+        cls.user_en = User.objects.create_user(
+            username='user_en', email='user.en@example.com', password='password123'
+        )
+        cls.user_en.profile.language = 'en'
+        cls.user_en.profile.save()
+
+        # Create Italian user
+        cls.user_it = User.objects.create_user(
+            username='user_it', email='user.it@example.com', password='password123'
+        )
+        cls.user_it.profile.language = 'it'
+        cls.user_it.profile.save()
+
+        # Create another Italian user for batching tests
+        cls.user_it2 = User.objects.create_user(
+            username='user_it2', email='user.it2@example.com', password='password123'
+        )
+        cls.user_it2.profile.language = 'it'
+        cls.user_it2.profile.save()
+
+    def test_get_user_language(self):
+        """Test resolving user language from profile, settings, and defaults."""
+        self.assertEqual(get_user_language(self.user_en), 'en')
+        self.assertEqual(get_user_language(self.user_it), 'it')
+
+        # Test user without language set falls back to system default
+        user_no_lang = User.objects.create_user(
+            username='user_no_lang', email='no.lang@example.com', password='password123'
+        )
+        user_no_lang.profile.language = None
+        user_no_lang.profile.save()
+
+        self.assertEqual(
+            get_user_language(user_no_lang), getattr(settings, 'LANGUAGE_CODE', 'en-us')
+        )
+
+        # Test user with InvenTreeUserSetting LANGUAGE override
+        with patch.object(InvenTreeUserSetting, 'get_setting', return_value='de'):
+            self.assertEqual(get_user_language(user_no_lang), 'de')
+
+    @patch('InvenTree.helpers_email.send_email')
+    def test_email_notifications_locale_translation(self, mock_send_email):
+        """Test that notification emails are translated according to recipient user locale."""
+        email_plugin = InvenTreeEmailNotifications()
+
+        context = {
+            'name': _('Items Received'),
+            'message': _('Items have been received against a purchase order'),
+            'template': {
+                'html': 'email/purchase_order_received.html',
+                'subject': _('Items Received'),
+            },
+            'link': 'http://localhost:8000/order/purchase-order/1/',
+        }
+
+        # Send notification to both English and Italian recipients
+        result = email_plugin.send_notification(
+            None, 'test', [self.user_en, self.user_it], context
+        )
+        self.assertTrue(result)
+
+        # Expect two distinct email dispatch calls (one per locale group)
+        self.assertEqual(mock_send_email.call_count, 2)
+
+        calls = mock_send_email.call_args_list
+
+        # Map dispatched emails by recipient email
+        dispatched_by_recipient = {}
+        for call in calls:
+            args, kwargs = call
+            subject = args[0]
+            recipients = args[2]
+            html_message = kwargs.get('html_message', '')
+            for r in recipients:
+                dispatched_by_recipient[r] = (subject, html_message)
+
+        # Assert English recipient received English text
+        self.assertIn(self.user_en.email, dispatched_by_recipient)
+        subject_en, html_en = dispatched_by_recipient[self.user_en.email]
+        self.assertIn('Items Received', subject_en)
+        self.assertIn('Items have been received against a purchase order', html_en)
+        self.assertIn('Click on the following link to view this order', html_en)
+
+        # Assert Italian recipient received translated Italian text
+        self.assertIn(self.user_it.email, dispatched_by_recipient)
+        subject_it, html_it = dispatched_by_recipient[self.user_it.email]
+        self.assertIn('Elemento ricevuto', subject_it)
+        self.assertIn(
+            'Gli elementi sono stati ricevuti a fronte di un ordine di acquisto',  # codespell:ignore
+            html_it,
+        )
+        self.assertIn("Clicca il seguente link per visualizzare quest'ordine", html_it)
+
+    @patch('InvenTree.helpers_email.send_email')
+    def test_email_notifications_single_locale_batching(self, mock_send_email):
+        """Test that recipients sharing the same locale are batched into a single email."""
+        email_plugin = InvenTreeEmailNotifications()
+
+        context = {
+            'template': {
+                'html': 'email/purchase_order_received.html',
+                'subject': _('Items Received'),
+            },
+            'message': _('Items have been received against a purchase order'),
+        }
+
+        result = email_plugin.send_notification(
+            None, 'test', [self.user_it, self.user_it2], context
+        )
+        self.assertTrue(result)
+
+        # Since both users are Italian, only a single email should be sent
+        self.assertEqual(mock_send_email.call_count, 1)
+
+        args, _kwargs = mock_send_email.call_args
+        recipients = args[2]
+        self.assertEqual(len(recipients), 2)
+        self.assertIn(self.user_it.email, recipients)
+        self.assertIn(self.user_it2.email, recipients)
+
+    def test_ui_notifications_locale_translation(self):
+        """Test that UI notification messages are saved with user-specific translations."""
+        ui_plugin = InvenTreeUINotifications()
+
+        context = {
+            'name': _('Items Received'),
+            'message': _('Items have been received against a purchase order'),
+            'link': 'http://localhost:8000/order/purchase-order/1/',
+        }
+
+        result = ui_plugin.send_notification(
+            self.user_en, 'test', [self.user_en, self.user_it], context
+        )
+        self.assertTrue(result)
+
+        # Verify English UI notification
+        msg_en = NotificationMessage.objects.filter(
+            user=self.user_en, category='test'
+        ).latest('pk')
+        self.assertEqual(msg_en.name, 'Items Received')
+        self.assertEqual(
+            msg_en.message, 'Items have been received against a purchase order'
+        )
+
+        # Verify Italian UI notification
+        msg_it = NotificationMessage.objects.filter(
+            user=self.user_it, category='test'
+        ).latest('pk')
+        self.assertEqual(msg_it.name, 'Elemento ricevuto')
+        self.assertEqual(
+            msg_it.message,
+            'Gli elementi sono stati ricevuti a fronte di un ordine di acquisto',  # codespell:ignore
+        )
+
+    def test_email_notifications_no_recipients(self):
+        """Test that email notification returns False when no valid recipients exist."""
+        email_plugin = InvenTreeEmailNotifications()
+
+        # No template in context
+        self.assertFalse(
+            email_plugin.send_notification(None, 'test', [self.user_en], {})
+        )
+
+        # Empty users list
+        self.assertFalse(
+            email_plugin.send_notification(
+                None, 'test', [], {'template': {'html': 'email/test_email.html'}}
+            )
+        )

src/backend/InvenTree/plugin/builtin/integration/core_notifications.py

@@ -1,15 +1,19 @@
 """Core set of Notifications as a Plugin."""
 
+from collections import defaultdict
+
 from django.conf import settings
 from django.contrib.auth.models import User
 from django.db.models import Model
 from django.template.loader import render_to_string
+from django.utils.translation import gettext, override
 from django.utils.translation import gettext_lazy as _
 
 import requests
 import structlog
 
 import InvenTree.helpers_email
+from common.notifications import get_user_language
 from common.settings import get_global_setting
 from plugin import InvenTreePlugin
 from plugin.mixins import NotificationMixin, SettingsMixin
@@ -43,16 +47,26 @@ class InvenTreeUINotifications(NotificationMixin, InvenTreePlugin):
         if not target:
             target = self.plugin_config()
 
-        # Bulk create notification messages for all provided users
+        # Bulk create notification messages for all provided users in their respective language context
         for user in users:
+            user_language = get_user_language(user)
+            with override(user_language):
+                name = ctx.get('name')
+                if name is not None:
+                    name = gettext(str(name))
+
+                message = ctx.get('message')
+                if message is not None:
+                    message = gettext(str(message))
+
             entries.append(
                 NotificationMessage(
                     target_object=target,
                     source_object=user,
                     user=user,
                     category=category,
-                    name=ctx.get('name'),
-                    message=ctx.get('message'),
+                    name=name,
+                    message=message,
                     link=ctx.get('link'),
                 )
             )
@@ -89,16 +103,8 @@ class InvenTreeEmailNotifications(NotificationMixin, SettingsMixin, InvenTreePlu
         if not context.get('template'):
             return False
 
-        html_message = render_to_string(context['template']['html'], context)
-
-        # Prefix the 'instance title' to the email subject
-        instance_title = get_global_setting('INVENTREE_INSTANCE')
-        subject = context['template'].get('subject', '')
-
-        if instance_title:
-            subject = f'[{instance_title}] {subject}'
-
-        recipients = []
+        # Group target users by their preferred language
+        language_groups: dict[str, list[str]] = defaultdict(list)
 
         for user in users:
             # Skip if the user does not want to receive email notifications
@@ -106,9 +112,34 @@ class InvenTreeEmailNotifications(NotificationMixin, SettingsMixin, InvenTreePlu
                 continue
 
             if email := InvenTree.helpers_email.get_email_for_user(user):
-                recipients.append(email)
+                user_language = get_user_language(user)
+                language_groups[user_language].append(email)
+
+        if not language_groups:
+            # No recipients found, so we cannot send the email
+            return False
+
+        instance_title = get_global_setting('INVENTREE_INSTANCE')
+        raw_subject = context['template'].get('subject', '')
+        template_name = context['template']['html']
+
+        for user_language, recipients in language_groups.items():
+            with override(user_language):
+                # Translate subject
+                subject = gettext(str(raw_subject))
+                if instance_title:
+                    subject = f'[{instance_title}] {subject}'
+
+                # Build localized context copy so template rendering evaluates strings in user locale
+                ctx = dict(context)
+                if 'name' in ctx and ctx['name'] is not None:
+                    ctx['name'] = gettext(str(ctx['name']))
+                if 'message' in ctx and ctx['message'] is not None:
+                    ctx['message'] = gettext(str(ctx['message']))
+
+                # Re-render html_message with translated strings and templates
+                html_message = render_to_string(template_name, ctx)
 
-        if recipients:
                 InvenTree.helpers_email.send_email(
                     subject,
                     '',
@@ -116,10 +147,8 @@ class InvenTreeEmailNotifications(NotificationMixin, SettingsMixin, InvenTreePlu
                     html_message=html_message,
                     force_async=not settings.TESTING,
                 )
-            return True
 
-        # No recipients found, so we cannot send the email
-        return False
+        return True
 
 
 class InvenTreeSlackNotifications(NotificationMixin, SettingsMixin, InvenTreePlugin):