diff --git a/i18n/default_de.json b/i18n/default_de.json
index 14cf1eb..86e5499 100644
--- a/i18n/default_de.json
+++ b/i18n/default_de.json
@@ -295,7 +295,6 @@
   "Profile image": "Profilbild",
   "Profile": "Profil",
   "Profile description": "Profilbeschreibung",
-  "About": "Über",
   "Info": "Info",
   "Search results": "Suchergebnisse",
   "Result": "Ergebnis",
@@ -470,10 +469,6 @@
   "Status & meta": "Status & Meta",
   "Audit": "Audit",
   "Overview": "Übersicht",
-  "Quick actions": "Schnellaktionen",
-  "Send email": "E-Mail senden",
-  "Call phone": "Telefon anrufen",
-  "Call mobile": "Mobil anrufen",
   "Choose color": "Farbe wählen",
   "Be careful - this resets the tenants color": "Achtung – das setzt die Primärfarbe des Mandanten zurück",
   "Code": "Code",
@@ -520,13 +515,11 @@
   "Department can not be created": "Abteilung kann nicht erstellt werden",
   "Department can not be updated": "Abteilung kann nicht aktualisiert werden",
   "Delete this department?": "Diese Abteilung wirklich löschen?",
-  "Delete this bookmark?": "Dieses Lesezeichen wirklich löschen?",
   "Delete department": "Abteilung löschen",
   "This will permanently delete this department.": "Diese Abteilung wird dauerhaft gelöscht.",
   "Assigned departments": "Zugewiesene Abteilungen",
   "Select departments": "Abteilungen auswählen",
   "Departments for tenant": "Abteilungen für Mandant",
-  "No departments": "Keine Abteilungen",
   "No departments available for this tenant": "Für diesen Mandanten sind keine Abteilungen verfügbar",
   "Assign tenants first to select departments": "Bitte zuerst Mandanten zuweisen, um Abteilungen auszuwählen",
   "No tenants available": "Keine Mandanten verfügbar",
@@ -549,7 +542,6 @@
   "Delete permission": "Berechtigung löschen",
   "This will permanently delete this role.": "Diese Rolle wird dauerhaft gelöscht.",
   "This will permanently delete this permission.": "Diese Berechtigung wird dauerhaft gelöscht.",
-  "This action cannot be undone.": "Diese Aktion kann nicht rückgängig gemacht werden.",
   "Description": "Beschreibung",
   "Description cannot be empty": "Beschreibung darf nicht leer sein",
   "Status is invalid": "Status ist ungültig",
@@ -647,7 +639,6 @@
   "SMTP security": "SMTP Sicherheit",
   "SMTP from address": "Absender-Adresse",
   "SMTP from name": "Absendername",
-  "Address book": "Adressbuch",
   "Mobile": "Mobil",
   "Short dial": "Kurzwahl",
   "setting.smtp_host": "SMTP-Serveradresse (z.B. smtp.example.com)",
@@ -659,7 +650,6 @@
   "setting.smtp_from_name": "Absendername für ausgehende Nachrichten",
   "High contrast": "Hoher Kontrast",
   "Toggle contrast": "Kontrast umschalten",
-  "View in address book": "Im Adressbuch ansehen",
   "Organization & Quality": "Organisation & Qualität",
   "Email security": "E-Mail Sicherheit",
   "API": "API",
@@ -813,8 +803,6 @@
   "Please fill required custom field: %s": "Bitte Pflicht-Zusatzfeld ausfüllen: %s",
   "Invalid value for %s": "Ungültiger Wert für %s",
   "Please select": "Bitte auswählen",
-  "From": "Von",
-  "To": "Bis",
   "perm.custom_fields.manage": "Mandanten-Zusatzfelder verwalten",
   "perm.custom_fields.edit_values": "Benutzer-Zusatzfelder bearbeiten",
   "Label": "Bezeichnung",
@@ -999,7 +987,6 @@
   "Import another file": "Weitere Datei importieren",
   "No row errors found": "Keine Zeilenfehler gefunden",
   "Row": "Zeile",
-  "Code": "Code",
   "Message": "Nachricht",
   "No upload file provided": "Keine Upload-Datei übergeben",
   "Upload exceeds the maximum size": "Upload überschreitet die maximale Dateigröße",
@@ -1212,7 +1199,6 @@
   "Actor tenant": "Akteur-Mandant",
   "Event details": "Ereignisdetails",
   "Target type": "Zieltyp",
-  "Request ID": "Request-ID",
   "IP hash": "IP-Hash",
   "User agent hash": "User-Agent-Hash",
   "Channel": "Kanal",
@@ -1299,45 +1285,5 @@
   "Session expiring": "Sitzung läuft ab",
   "Your session will expire in {countdown}. Would you like to continue?": "Ihre Sitzung läuft in {countdown} ab. Möchten Sie fortfahren?",
   "Extend session": "Sitzung verlängern",
-  "Log out": "Abmelden",
-  "Bookmarks": "Lesezeichen",
-  "Bookmark this page": "Seite als Lesezeichen speichern",
-  "Save bookmark": "Lesezeichen speichern",
-  "Bookmark name": "Lesezeichen-Name",
-  "Delete bookmark": "Lesezeichen löschen",
-  "No bookmarks yet": "Noch keine Lesezeichen",
-  "New group": "Neue Gruppe",
-  "No group": "Keine Gruppe",
-  "Assign to group": "Gruppe zuweisen",
-  "Group name": "Gruppenname",
-  "Delete group": "Gruppe löschen",
-  "Group": "Gruppe",
-  "Icon": "Symbol",
-  "Maximum bookmarks reached": "Maximale Anzahl an Lesezeichen erreicht",
-  "Edit bookmark": "Lesezeichen bearbeiten",
-  "Save changes": "Änderungen speichern",
-  "Bookmark saved": "Lesezeichen gespeichert",
-  "Bookmark updated": "Lesezeichen aktualisiert",
-  "Bookmark deleted": "Lesezeichen gelöscht",
-  "Group created": "Gruppe erstellt",
-  "Group deleted": "Gruppe gelöscht",
-  "Group delete failed": "Gruppe konnte nicht gelöscht werden",
-  "Delete group and keep bookmarks?": "Gruppe löschen und enthaltene Lesezeichen behalten?",
-  "Bookmark action failed": "Lesezeichen-Aktion fehlgeschlagen",
-  "Group action failed": "Gruppen-Aktion fehlgeschlagen",
-  "Reorder saved": "Sortierung gespeichert",
-  "Reorder failed": "Sortierung fehlgeschlagen",
-  "Move group up": "Gruppe nach oben",
-  "Move group down": "Gruppe nach unten",
-  "Move bookmark up": "Lesezeichen nach oben",
-  "Move bookmark down": "Lesezeichen nach unten",
-  "Group actions": "Gruppenaktionen",
-  "Bookmark actions": "Lesezeichenaktionen",
-  "Bookmark name is required": "Lesezeichen-Name ist erforderlich",
-  "Bookmark URL is invalid": "Lesezeichen-URL ist ungültig",
-  "Group not found": "Gruppe nicht gefunden",
-  "Edit group": "Gruppe bearbeiten",
-  "Group updated": "Gruppe aktualisiert",
-  "Group name is required": "Gruppenname ist erforderlich",
-  "Maximum groups reached": "Maximale Anzahl an Gruppen erreicht"
+  "Log out": "Abmelden"
 }
diff --git a/i18n/default_en.json b/i18n/default_en.json
index 54de160..ff41ad2 100644
--- a/i18n/default_en.json
+++ b/i18n/default_en.json
@@ -295,7 +295,6 @@
   "Profile image": "Profile image",
   "Profile": "Profile",
   "Profile description": "Profile description",
-  "About": "About",
   "Info": "Info",
   "Search results": "Search results",
   "Result": "Result",
@@ -470,10 +469,6 @@
   "Status & meta": "Status & meta",
   "Audit": "Audit",
   "Overview": "Overview",
-  "Quick actions": "Quick actions",
-  "Send email": "Send email",
-  "Call phone": "Call phone",
-  "Call mobile": "Call mobile",
   "Choose color": "Choose color",
   "Be careful - this resets the tenants color": "Be careful - this resets the tenant color",
   "Code": "Code",
@@ -520,13 +515,11 @@
   "Department can not be created": "Department can not be created",
   "Department can not be updated": "Department can not be updated",
   "Delete this department?": "Delete this department?",
-  "Delete this bookmark?": "Delete this bookmark?",
   "Delete department": "Delete department",
   "This will permanently delete this department.": "This will permanently delete this department.",
   "Assigned departments": "Assigned departments",
   "Select departments": "Select departments",
   "Departments for tenant": "Departments for tenant",
-  "No departments": "No departments",
   "No departments available for this tenant": "No departments available for this tenant",
   "Assign tenants first to select departments": "Assign tenants first to select departments",
   "No tenants available": "No tenants available",
@@ -549,7 +542,6 @@
   "Delete permission": "Delete permission",
   "This will permanently delete this role.": "This will permanently delete this role.",
   "This will permanently delete this permission.": "This will permanently delete this permission.",
-  "This action cannot be undone.": "This action cannot be undone.",
   "Description": "Description",
   "Description cannot be empty": "Description cannot be empty",
   "Status is invalid": "Status is invalid",
@@ -647,7 +639,6 @@
   "SMTP security": "SMTP security",
   "SMTP from address": "SMTP from address",
   "SMTP from name": "SMTP from name",
-  "Address book": "Address book",
   "Mobile": "Mobile",
   "Short dial": "Short dial",
   "setting.smtp_host": "SMTP server host (e.g. smtp.example.com)",
@@ -659,7 +650,6 @@
   "setting.smtp_from_name": "From name for outgoing emails",
   "High contrast": "High contrast",
   "Toggle contrast": "Toggle contrast",
-  "View in address book": "View in address book",
   "Organization & Quality": "Organization & Quality",
   "Email security": "Email security",
   "API": "API",
@@ -813,8 +803,6 @@
   "Please fill required custom field: %s": "Please fill required custom field: %s",
   "Invalid value for %s": "Invalid value for %s",
   "Please select": "Please select",
-  "From": "From",
-  "To": "To",
   "perm.custom_fields.manage": "Manage tenant custom fields",
   "perm.custom_fields.edit_values": "Edit user custom field values",
   "Label": "Label",
@@ -999,7 +987,6 @@
   "Import another file": "Import another file",
   "No row errors found": "No row errors found",
   "Row": "Row",
-  "Code": "Code",
   "Message": "Message",
   "No upload file provided": "No upload file provided",
   "Upload exceeds the maximum size": "Upload exceeds the maximum size",
@@ -1212,7 +1199,6 @@
   "Actor tenant": "Actor tenant",
   "Event details": "Event details",
   "Target type": "Target type",
-  "Request ID": "Request ID",
   "IP hash": "IP hash",
   "User agent hash": "User agent hash",
   "Channel": "Channel",
@@ -1299,45 +1285,5 @@
   "Session expiring": "Session expiring",
   "Your session will expire in {countdown}. Would you like to continue?": "Your session will expire in {countdown}. Would you like to continue?",
   "Extend session": "Extend session",
-  "Log out": "Log out",
-  "Bookmarks": "Bookmarks",
-  "Bookmark this page": "Bookmark this page",
-  "Save bookmark": "Save bookmark",
-  "Bookmark name": "Bookmark name",
-  "Delete bookmark": "Delete bookmark",
-  "No bookmarks yet": "No bookmarks yet",
-  "New group": "New group",
-  "No group": "No group",
-  "Assign to group": "Assign to group",
-  "Group name": "Group name",
-  "Delete group": "Delete group",
-  "Group": "Group",
-  "Icon": "Icon",
-  "Maximum bookmarks reached": "Maximum bookmarks reached",
-  "Edit bookmark": "Edit bookmark",
-  "Save changes": "Save changes",
-  "Bookmark saved": "Bookmark saved",
-  "Bookmark updated": "Bookmark updated",
-  "Bookmark deleted": "Bookmark deleted",
-  "Group created": "Group created",
-  "Group deleted": "Group deleted",
-  "Group delete failed": "Group delete failed",
-  "Delete group and keep bookmarks?": "Delete group and keep bookmarks?",
-  "Bookmark action failed": "Bookmark action failed",
-  "Group action failed": "Group action failed",
-  "Reorder saved": "Reorder saved",
-  "Reorder failed": "Reorder failed",
-  "Move group up": "Move group up",
-  "Move group down": "Move group down",
-  "Move bookmark up": "Move bookmark up",
-  "Move bookmark down": "Move bookmark down",
-  "Group actions": "Group actions",
-  "Bookmark actions": "Bookmark actions",
-  "Bookmark name is required": "Bookmark name is required",
-  "Bookmark URL is invalid": "Bookmark URL is invalid",
-  "Group not found": "Group not found",
-  "Edit group": "Edit group",
-  "Group updated": "Group updated",
-  "Group name is required": "Group name is required",
-  "Maximum groups reached": "Maximum groups reached"
+  "Log out": "Log out"
 }
diff --git a/lib/App/Module/ModuleI18nLoader.php b/lib/App/Module/ModuleI18nLoader.php
new file mode 100644
index 0000000..91e72cf
--- /dev/null
+++ b/lib/App/Module/ModuleI18nLoader.php
@@ -0,0 +1,55 @@
+<?php
+
+namespace MintyPHP\App\Module;
+
+use MintyPHP\I18n;
+use ReflectionProperty;
+
+/**
+ * Preloads core + module translations into I18n::$strings at boot time.
+ *
+ * Since I18n::$strings is private static and lives in a vendor class,
+ * Reflection is used once per locale to inject the merged translation map.
+ */
+final class ModuleI18nLoader
+{
+    /**
+     * @param list<ModuleManifest> $manifests Active module manifests (already sorted)
+     * @param string $coreI18nDir Absolute path to the core i18n/ directory
+     */
+    public static function preload(array $manifests, string $coreI18nDir): void
+    {
+        $locales = ['de', 'en'];
+        $domain = I18n::$domain ?: 'default';
+
+        $prop = new ReflectionProperty(I18n::class, 'strings');
+
+        foreach ($locales as $locale) {
+            // Load core file
+            $coreFile = $coreI18nDir . '/' . $domain . '_' . $locale . '.json';
+            $merged = is_file($coreFile)
+                ? (json_decode(file_get_contents($coreFile), true) ?: [])
+                : [];
+
+            // Merge each module's translations on top
+            foreach ($manifests as $manifest) {
+                if ($manifest->i18nPath === null) {
+                    continue;
+                }
+                $moduleFile = $manifest->i18nPath . '/' . $domain . '_' . $locale . '.json';
+                if (!is_file($moduleFile)) {
+                    continue;
+                }
+                $moduleStrings = json_decode(file_get_contents($moduleFile), true);
+                if (is_array($moduleStrings)) {
+                    $merged = array_merge($merged, $moduleStrings);
+                }
+            }
+
+            // Inject via Reflection into I18n::$strings
+            $strings = $prop->getValue();
+            $strings[$domain][$locale] = $merged;
+            $prop->setValue(null, $strings);
+        }
+    }
+}
diff --git a/lib/App/Module/ModuleManifest.php b/lib/App/Module/ModuleManifest.php
index f4552aa..e07db7d 100644
--- a/lib/App/Module/ModuleManifest.php
+++ b/lib/App/Module/ModuleManifest.php
@@ -83,6 +83,8 @@ final class ModuleManifest
 
     public readonly ?string $migrationsPath;
 
+    public readonly ?string $i18nPath;
+
     public readonly string $basePath;
 
     /**
@@ -128,6 +130,11 @@ final class ModuleManifest
         $this->migrationsPath = is_string($migrationsPath) && trim($migrationsPath) !== ''
             ? rtrim($basePath, '/') . '/' . ltrim(trim($migrationsPath), '/')
             : null;
+
+        $i18nPath = $raw['i18n_path'] ?? null;
+        $this->i18nPath = is_string($i18nPath) && trim($i18nPath) !== ''
+            ? rtrim($basePath, '/') . '/' . ltrim(trim($i18nPath), '/')
+            : null;
     }
 
     /**
diff --git a/lib/App/Module/ModuleRegistry.php b/lib/App/Module/ModuleRegistry.php
index 6759925..cb12a7a 100644
--- a/lib/App/Module/ModuleRegistry.php
+++ b/lib/App/Module/ModuleRegistry.php
@@ -148,6 +148,12 @@ final class ModuleRegistry
         // module classes (MintyPHP\Module\<Name>\*) resolve without a custom loader.
         self::registerModuleAutoloading($manifests);
 
+        // Preload core + module translations into I18n before any t() call.
+        $coreI18nDir = rtrim($modulesDir, '/') . '/../i18n';
+        if (is_dir($coreI18nDir)) {
+            ModuleI18nLoader::preload($manifests, $coreI18nDir);
+        }
+
         // Register and merge
         foreach ($manifests as $manifest) {
             $registry->registerModule($manifest);
diff --git a/modules/addressbook/i18n/default_de.json b/modules/addressbook/i18n/default_de.json
new file mode 100644
index 0000000..38279d5
--- /dev/null
+++ b/modules/addressbook/i18n/default_de.json
@@ -0,0 +1,12 @@
+{
+  "About": "Über",
+  "Address book": "Adressbuch",
+  "Call mobile": "Mobil anrufen",
+  "Call phone": "Telefon anrufen",
+  "From": "Von",
+  "No departments": "Keine Abteilungen",
+  "Quick actions": "Schnellaktionen",
+  "Send email": "E-Mail senden",
+  "To": "Bis",
+  "View in address book": "Im Adressbuch ansehen"
+}
diff --git a/modules/addressbook/i18n/default_en.json b/modules/addressbook/i18n/default_en.json
new file mode 100644
index 0000000..10dc3a5
--- /dev/null
+++ b/modules/addressbook/i18n/default_en.json
@@ -0,0 +1,12 @@
+{
+  "About": "About",
+  "Address book": "Address book",
+  "Call mobile": "Call mobile",
+  "Call phone": "Call phone",
+  "From": "From",
+  "No departments": "No departments",
+  "Quick actions": "Quick actions",
+  "Send email": "Send email",
+  "To": "To",
+  "View in address book": "View in address book"
+}
diff --git a/modules/addressbook/module.php b/modules/addressbook/module.php
index 46fc9a7..5a2ba16 100644
--- a/modules/addressbook/module.php
+++ b/modules/addressbook/module.php
@@ -94,4 +94,5 @@ return [
     ],
 
     'migrations_path' => 'db/updates',
+    'i18n_path' => 'i18n',
 ];
diff --git a/modules/bookmarks/i18n/default_de.json b/modules/bookmarks/i18n/default_de.json
new file mode 100644
index 0000000..5f97e3a
--- /dev/null
+++ b/modules/bookmarks/i18n/default_de.json
@@ -0,0 +1,43 @@
+{
+  "Bookmarks": "Lesezeichen",
+  "Bookmark this page": "Seite als Lesezeichen speichern",
+  "Save bookmark": "Lesezeichen speichern",
+  "Bookmark name": "Lesezeichen-Name",
+  "Delete bookmark": "Lesezeichen löschen",
+  "Delete this bookmark?": "Dieses Lesezeichen wirklich löschen?",
+  "No bookmarks yet": "Noch keine Lesezeichen",
+  "New group": "Neue Gruppe",
+  "No group": "Keine Gruppe",
+  "Assign to group": "Gruppe zuweisen",
+  "Group name": "Gruppenname",
+  "Delete group": "Gruppe löschen",
+  "Group": "Gruppe",
+  "Icon": "Symbol",
+  "Maximum bookmarks reached": "Maximale Anzahl an Lesezeichen erreicht",
+  "Edit bookmark": "Lesezeichen bearbeiten",
+  "Save changes": "Änderungen speichern",
+  "Bookmark saved": "Lesezeichen gespeichert",
+  "Bookmark updated": "Lesezeichen aktualisiert",
+  "Bookmark deleted": "Lesezeichen gelöscht",
+  "Group created": "Gruppe erstellt",
+  "Group deleted": "Gruppe gelöscht",
+  "Group delete failed": "Gruppe konnte nicht gelöscht werden",
+  "Delete group and keep bookmarks?": "Gruppe löschen und enthaltene Lesezeichen behalten?",
+  "Bookmark action failed": "Lesezeichen-Aktion fehlgeschlagen",
+  "Group action failed": "Gruppen-Aktion fehlgeschlagen",
+  "Reorder saved": "Sortierung gespeichert",
+  "Reorder failed": "Sortierung fehlgeschlagen",
+  "Move group up": "Gruppe nach oben",
+  "Move group down": "Gruppe nach unten",
+  "Move bookmark up": "Lesezeichen nach oben",
+  "Move bookmark down": "Lesezeichen nach unten",
+  "Group actions": "Gruppenaktionen",
+  "Bookmark actions": "Lesezeichenaktionen",
+  "Bookmark name is required": "Lesezeichen-Name ist erforderlich",
+  "Bookmark URL is invalid": "Lesezeichen-URL ist ungültig",
+  "Group not found": "Gruppe nicht gefunden",
+  "Edit group": "Gruppe bearbeiten",
+  "Group updated": "Gruppe aktualisiert",
+  "Group name is required": "Gruppenname ist erforderlich",
+  "Maximum groups reached": "Maximale Anzahl an Gruppen erreicht"
+}
diff --git a/modules/bookmarks/i18n/default_en.json b/modules/bookmarks/i18n/default_en.json
new file mode 100644
index 0000000..5928564
--- /dev/null
+++ b/modules/bookmarks/i18n/default_en.json
@@ -0,0 +1,43 @@
+{
+  "Bookmarks": "Bookmarks",
+  "Bookmark this page": "Bookmark this page",
+  "Save bookmark": "Save bookmark",
+  "Bookmark name": "Bookmark name",
+  "Delete bookmark": "Delete bookmark",
+  "Delete this bookmark?": "Delete this bookmark?",
+  "No bookmarks yet": "No bookmarks yet",
+  "New group": "New group",
+  "No group": "No group",
+  "Assign to group": "Assign to group",
+  "Group name": "Group name",
+  "Delete group": "Delete group",
+  "Group": "Group",
+  "Icon": "Icon",
+  "Maximum bookmarks reached": "Maximum bookmarks reached",
+  "Edit bookmark": "Edit bookmark",
+  "Save changes": "Save changes",
+  "Bookmark saved": "Bookmark saved",
+  "Bookmark updated": "Bookmark updated",
+  "Bookmark deleted": "Bookmark deleted",
+  "Group created": "Group created",
+  "Group deleted": "Group deleted",
+  "Group delete failed": "Group delete failed",
+  "Delete group and keep bookmarks?": "Delete group and keep bookmarks?",
+  "Bookmark action failed": "Bookmark action failed",
+  "Group action failed": "Group action failed",
+  "Reorder saved": "Reorder saved",
+  "Reorder failed": "Reorder failed",
+  "Move group up": "Move group up",
+  "Move group down": "Move group down",
+  "Move bookmark up": "Move bookmark up",
+  "Move bookmark down": "Move bookmark down",
+  "Group actions": "Group actions",
+  "Bookmark actions": "Bookmark actions",
+  "Bookmark name is required": "Bookmark name is required",
+  "Bookmark URL is invalid": "Bookmark URL is invalid",
+  "Group not found": "Group not found",
+  "Edit group": "Edit group",
+  "Group updated": "Group updated",
+  "Group name is required": "Group name is required",
+  "Maximum groups reached": "Maximum groups reached"
+}
diff --git a/modules/bookmarks/module.php b/modules/bookmarks/module.php
index dda6bcc..5b605a7 100644
--- a/modules/bookmarks/module.php
+++ b/modules/bookmarks/module.php
@@ -130,4 +130,5 @@ return [
 
     'permissions' => [],
     'migrations_path' => null,
+    'i18n_path' => 'i18n',
 ];
diff --git a/modules/notifications/i18n/default_de.json b/modules/notifications/i18n/default_de.json
new file mode 100644
index 0000000..a31062c
--- /dev/null
+++ b/modules/notifications/i18n/default_de.json
@@ -0,0 +1,10 @@
+{
+  "Notifications": "Benachrichtigungen",
+  "No notifications": "Keine Benachrichtigungen",
+  "Mark all as read": "Alle als gelesen markieren",
+  "Mark as read": "Als gelesen markieren",
+  "Dismiss": "Verwerfen",
+  "Action failed": "Aktion fehlgeschlagen",
+  "New user: %s": "Neuer Benutzer: %s",
+  "User deleted: %s": "Benutzer gelöscht: %s"
+}
diff --git a/modules/notifications/i18n/default_en.json b/modules/notifications/i18n/default_en.json
new file mode 100644
index 0000000..a0dba59
--- /dev/null
+++ b/modules/notifications/i18n/default_en.json
@@ -0,0 +1,10 @@
+{
+  "Notifications": "Notifications",
+  "No notifications": "No notifications",
+  "Mark all as read": "Mark all as read",
+  "Mark as read": "Mark as read",
+  "Dismiss": "Dismiss",
+  "Action failed": "Action failed",
+  "New user: %s": "New user: %s",
+  "User deleted: %s": "User deleted: %s"
+}
diff --git a/modules/notifications/module.php b/modules/notifications/module.php
new file mode 100644
index 0000000..7e11510
--- /dev/null
+++ b/modules/notifications/module.php
@@ -0,0 +1,115 @@
+<?php
+
+/**
+ * Notifications module manifest.
+ *
+ * In-app notifications with bell icon, dropdown panel,
+ * event-driven creation, and scheduled cleanup.
+ */
+return [
+    'id' => 'notifications',
+    'version' => '1.0.0',
+    'enabled_by_default' => true,
+    'load_order' => 15,
+    'requires' => [],
+
+    'routes' => [
+        ['path' => 'notifications/list-data', 'target' => 'notifications/list-data'],
+        ['path' => 'notifications/mark-read-data', 'target' => 'notifications/mark-read-data'],
+        ['path' => 'notifications/delete-data', 'target' => 'notifications/delete-data'],
+        ['path' => 'notifications/unread-count-data', 'target' => 'notifications/unread-count-data'],
+    ],
+    'public_paths' => [],
+
+    'container_registrars' => [
+        \MintyPHP\Module\Notifications\NotificationsContainerRegistrar::class,
+    ],
+
+    'ui_slots' => [
+        'topbar.right_item' => [
+            [
+                'key' => 'notifications-bell',
+                'template' => 'templates/topbar-notification-bell.phtml',
+                'permission' => 'notifications.view',
+                'order' => 100,
+            ],
+        ],
+        'layout.head_style' => [
+            [
+                'key' => 'notifications-topbar-style',
+                'path' => 'modules/notifications/css/layout/app-topbar-notifications.css',
+                'permission' => 'notifications.view',
+                'order' => 100,
+            ],
+            [
+                'key' => 'notifications-dropdown-style',
+                'path' => 'modules/notifications/css/components/app-notification-dropdown.css',
+                'permission' => 'notifications.view',
+                'order' => 101,
+            ],
+        ],
+        'runtime.component' => [
+            [
+                'key' => 'notification-bell',
+                'script' => 'modules/notifications/js/components/app-notification-bell.js',
+                'export' => 'initNotificationBell',
+                'scope' => 'global',
+                'config_path' => 'components.notificationBell',
+                'default_config' => [],
+                'phase' => 'late',
+                'permission' => 'notifications.view',
+                'order' => 100,
+            ],
+        ],
+    ],
+
+    'authorization_policies' => [
+        \MintyPHP\Module\Notifications\NotificationsAuthorizationPolicy::class,
+    ],
+
+    'permissions' => [
+        [
+            'key' => 'notifications.view',
+            'label' => 'Notifications: View',
+            'description' => 'View and manage own notifications',
+        ],
+    ],
+
+    'event_listeners' => [
+        'user.created' => [
+            ['class' => \MintyPHP\Module\Notifications\Listeners\UserCreatedNotificationListener::class, 'method' => 'handle'],
+        ],
+        'user.deleted' => [
+            ['class' => \MintyPHP\Module\Notifications\Listeners\UserDeletedNotificationListener::class, 'method' => 'handle'],
+        ],
+    ],
+
+    'scheduler_jobs' => [
+        [
+            'job_key' => 'notifications_cleanup',
+            'handler' => \MintyPHP\Module\Notifications\Handler\NotificationCleanupJobHandler::class,
+            'label' => 'Notification cleanup',
+            'description' => 'Purges read notifications older than 90 days',
+            'default_enabled' => 1,
+            'default_timezone' => 'UTC',
+            'default_schedule_type' => 'daily',
+            'default_schedule_interval' => 1,
+            'default_schedule_time' => '04:00',
+            'default_schedule_weekdays_csv' => null,
+            'default_catchup_once' => 1,
+            'allowed_schedule_types' => ['daily', 'weekly'],
+        ],
+    ],
+
+    'layout_context_providers' => [
+        \MintyPHP\Module\Notifications\Providers\NotificationsLayoutProvider::class,
+    ],
+    'session_providers' => [
+        \MintyPHP\Module\Notifications\Providers\NotificationsSessionProvider::class,
+    ],
+
+    'search_resources' => [],
+    'asset_groups' => [],
+    'migrations_path' => 'db/updates',
+    'i18n_path' => 'i18n',
+];
diff --git a/tests/Architecture/ModuleI18nContractTest.php b/tests/Architecture/ModuleI18nContractTest.php
new file mode 100644
index 0000000..374dfe9
--- /dev/null
+++ b/tests/Architecture/ModuleI18nContractTest.php
@@ -0,0 +1,127 @@
+<?php
+
+namespace MintyPHP\Tests\Architecture;
+
+use PHPUnit\Framework\Attributes\DataProvider;
+use PHPUnit\Framework\TestCase;
+
+/**
+ * GR-UI-015 (module extension): Every module with an i18n_path must ship
+ * matching default_de.json and default_en.json with identical keys and
+ * non-empty values.
+ */
+class ModuleI18nContractTest extends TestCase
+{
+    use ProjectFileAssertionSupport;
+
+    /**
+     * @return list<array{string, string}>
+     */
+    public static function moduleProvider(): array
+    {
+        $root = realpath(__DIR__ . '/../..');
+        if ($root === false) {
+            return [];
+        }
+
+        $modules = [];
+        foreach (glob($root . '/modules/*/module.php') as $manifestFile) {
+            $raw = (static function (string $path): mixed {
+                return require $path;
+            })($manifestFile);
+            if (!is_array($raw)) {
+                continue;
+            }
+            $i18nPath = $raw['i18n_path'] ?? null;
+            if (!is_string($i18nPath) || trim($i18nPath) === '') {
+                continue;
+            }
+            $moduleDir = dirname($manifestFile);
+            $moduleId = basename($moduleDir);
+            $resolvedPath = rtrim($moduleDir, '/') . '/' . ltrim(trim($i18nPath), '/');
+            $modules[$moduleId] = [$moduleId, $resolvedPath];
+        }
+
+        return $modules;
+    }
+
+    #[DataProvider('moduleProvider')]
+    public function testModuleI18nFilesExistAndAreValidJson(string $moduleId, string $i18nPath): void
+    {
+        $this->assertDirectoryExists($i18nPath, "Module '{$moduleId}' declares i18n_path but directory does not exist.");
+
+        $deFile = $i18nPath . '/default_de.json';
+        $enFile = $i18nPath . '/default_en.json';
+
+        $this->assertFileExists($deFile, "Module '{$moduleId}' is missing default_de.json");
+        $this->assertFileExists($enFile, "Module '{$moduleId}' is missing default_en.json");
+
+        $deRaw = file_get_contents($deFile);
+        $enRaw = file_get_contents($enFile);
+        $this->assertNotFalse($deRaw);
+        $this->assertNotFalse($enRaw);
+
+        $this->assertIsArray(json_decode($deRaw, true), "Module '{$moduleId}' default_de.json is not valid JSON");
+        $this->assertIsArray(json_decode($enRaw, true), "Module '{$moduleId}' default_en.json is not valid JSON");
+    }
+
+    #[DataProvider('moduleProvider')]
+    public function testModuleI18nKeyParity(string $moduleId, string $i18nPath): void
+    {
+        $de = $this->loadModuleKeys($i18nPath . '/default_de.json');
+        $en = $this->loadModuleKeys($i18nPath . '/default_en.json');
+
+        $missingInEn = array_values(array_diff($de, $en));
+        $this->assertSame(
+            [],
+            $missingInEn,
+            "Module '{$moduleId}' default_de.json keys missing from default_en.json:\n" . implode("\n", $missingInEn)
+        );
+
+        $missingInDe = array_values(array_diff($en, $de));
+        $this->assertSame(
+            [],
+            $missingInDe,
+            "Module '{$moduleId}' default_en.json keys missing from default_de.json:\n" . implode("\n", $missingInDe)
+        );
+    }
+
+    #[DataProvider('moduleProvider')]
+    public function testModuleI18nValuesAreNonEmpty(string $moduleId, string $i18nPath): void
+    {
+        foreach (['default_de.json', 'default_en.json'] as $file) {
+            $path = $i18nPath . '/' . $file;
+            if (!is_file($path)) {
+                continue;
+            }
+            $data = json_decode(file_get_contents($path), true);
+            $this->assertIsArray($data);
+
+            $empty = array_keys(array_filter($data, static fn ($v): bool => trim((string) $v) === ''));
+            $this->assertSame(
+                [],
+                $empty,
+                "Module '{$moduleId}' {$file} has empty values:\n" . implode("\n", $empty)
+            );
+        }
+    }
+
+    /**
+     * @return list<string>
+     */
+    private function loadModuleKeys(string $path): array
+    {
+        if (!is_file($path)) {
+            return [];
+        }
+        $data = json_decode(file_get_contents($path), true);
+        if (!is_array($data)) {
+            return [];
+        }
+
+        $keys = array_keys($data);
+        sort($keys, SORT_STRING);
+
+        return $keys;
+    }
+}
diff --git a/tests/I18n/TranslationKeysTest.php b/tests/I18n/TranslationKeysTest.php
index 20742b8..bc90805 100644
--- a/tests/I18n/TranslationKeysTest.php
+++ b/tests/I18n/TranslationKeysTest.php
@@ -13,7 +13,8 @@ class TranslationKeysTest extends TestCase
         $root = realpath(__DIR__ . '/../..');
         $this->assertNotFalse($root, 'Project root not found.');
 
-        $paths = [
+        // Core scan paths
+        $corePaths = [
             $root . '/pages',
             $root . '/templates',
             $root . '/lib',
@@ -21,6 +22,108 @@ class TranslationKeysTest extends TestCase
         ];
         $extensions = ['php', 'phtml', 'js'];
 
+        // Collect core keys
+        $coreKeys = $this->collectKeysFromPaths($corePaths, $extensions);
+
+        // Load core translations
+        $coreTranslations = $this->loadTranslationMap($root . '/i18n', ['default_de.json', 'default_en.json']);
+
+        // Also load all module translations so core keys provided by modules are available
+        $moduleTranslations = $this->loadAllModuleTranslations($root . '/modules');
+        $mergedTranslations = [];
+        foreach ($coreTranslations as $name => $map) {
+            $mergedTranslations[$name] = $map;
+        }
+        foreach ($moduleTranslations as $name => $maps) {
+            foreach ($maps as $locale => $map) {
+                $mergedTranslations[$locale] = array_merge($mergedTranslations[$locale] ?? [], $map);
+            }
+        }
+
+        // Validate core keys exist in merged (core + module) translations
+        $missing = [];
+        foreach ($coreKeys as $key) {
+            foreach ($mergedTranslations as $name => $map) {
+                if (!array_key_exists($key, $map)) {
+                    $missing[$name][] = $key;
+                }
+            }
+        }
+
+        $messages = [];
+        foreach ($missing as $name => $keys) {
+            $messages[] = $name . ' missing: ' . implode(', ', $keys);
+        }
+        $this->assertSame([], $missing, implode(' | ', $messages));
+    }
+
+    public function testAllModuleTranslationKeysExist(): void
+    {
+        $root = realpath(__DIR__ . '/../..');
+        $this->assertNotFalse($root, 'Project root not found.');
+
+        $modulesDir = $root . '/modules';
+        if (!is_dir($modulesDir)) {
+            $this->markTestSkipped('No modules directory found.');
+        }
+
+        $extensions = ['php', 'phtml', 'js'];
+
+        // Load core translations as fallback
+        $coreTranslations = $this->loadTranslationMap($root . '/i18n', ['default_de.json', 'default_en.json']);
+
+        $allMissing = [];
+
+        foreach (glob($modulesDir . '/*/module.php') as $manifestFile) {
+            $moduleDir = dirname($manifestFile);
+            $moduleId = basename($moduleDir);
+
+            // Scan module directories for keys
+            $modulePaths = [
+                $moduleDir . '/pages',
+                $moduleDir . '/templates',
+                $moduleDir . '/lib',
+                $moduleDir . '/web',
+            ];
+            $moduleKeys = $this->collectKeysFromPaths($modulePaths, $extensions);
+            if ($moduleKeys === []) {
+                continue;
+            }
+
+            // Load module translations and merge with core
+            $moduleI18nDir = $moduleDir . '/i18n';
+            $moduleTranslations = is_dir($moduleI18nDir)
+                ? $this->loadTranslationMap($moduleI18nDir, ['default_de.json', 'default_en.json'])
+                : [];
+
+            $merged = [];
+            foreach ($coreTranslations as $locale => $map) {
+                $merged[$locale] = array_merge($map, $moduleTranslations[$locale] ?? []);
+            }
+
+            foreach ($moduleKeys as $key) {
+                foreach ($merged as $locale => $map) {
+                    if (!array_key_exists($key, $map)) {
+                        $allMissing["modules/{$moduleId} → {$locale}"][] = $key;
+                    }
+                }
+            }
+        }
+
+        $messages = [];
+        foreach ($allMissing as $context => $keys) {
+            $messages[] = $context . ' missing: ' . implode(', ', $keys);
+        }
+        $this->assertSame([], $allMissing, implode(' | ', $messages));
+    }
+
+    /**
+     * @param list<string> $paths
+     * @param list<string> $extensions
+     * @return list<string>
+     */
+    private function collectKeysFromPaths(array $paths, array $extensions): array
+    {
         $usedKeys = [];
         foreach ($paths as $path) {
             if (!is_dir($path)) {
@@ -45,40 +148,71 @@ class TranslationKeysTest extends TestCase
             }
         }
 
-        $usedKeys = array_keys($usedKeys);
-        sort($usedKeys);
+        $keys = array_keys($usedKeys);
+        sort($keys);
 
-        $locales = [
-            'default_de.json' => $root . '/i18n/default_de.json',
-            'default_en.json' => $root . '/i18n/default_en.json',
-        ];
+        return $keys;
+    }
+
+    /**
+     * @param list<string> $files
+     * @return array<string, array<string, string>>
+     */
+    private function loadTranslationMap(string $dir, array $files): array
+    {
         $translations = [];
-        foreach ($locales as $name => $path) {
-            $this->assertFileExists($path, 'Missing locale file: ' . $name);
+        foreach ($files as $name) {
+            $path = $dir . '/' . $name;
+            if (!is_file($path)) {
+                continue;
+            }
             $raw = file_get_contents($path);
-            $this->assertNotFalse($raw, 'Failed to read locale file: ' . $name);
+            if ($raw === false) {
+                continue;
+            }
             $json = json_decode($raw, true);
-            $this->assertIsArray($json, 'Invalid JSON in locale file: ' . $name);
-            $translations[$name] = $json;
+            if (is_array($json)) {
+                $translations[$name] = $json;
+            }
         }
 
-        $missing = [];
-        foreach ($usedKeys as $key) {
-            foreach ($translations as $name => $map) {
-                if (!array_key_exists($key, $map)) {
-                    $missing[$name][] = $key;
+        return $translations;
+    }
+
+    /**
+     * @return array<string, array<string, array<string, string>>>
+     */
+    private function loadAllModuleTranslations(string $modulesDir): array
+    {
+        $result = [];
+        if (!is_dir($modulesDir)) {
+            return $result;
+        }
+
+        foreach (glob($modulesDir . '/*/i18n') as $i18nDir) {
+            $moduleId = basename(dirname($i18nDir));
+            foreach (['default_de.json', 'default_en.json'] as $file) {
+                $path = $i18nDir . '/' . $file;
+                if (!is_file($path)) {
+                    continue;
+                }
+                $raw = file_get_contents($path);
+                if ($raw === false) {
+                    continue;
+                }
+                $json = json_decode($raw, true);
+                if (is_array($json)) {
+                    $result[$moduleId][$file] = $json;
                 }
             }
         }
 
-        $messages = [];
-        foreach ($missing as $name => $keys) {
-            $messages[] = $name . ' missing: ' . implode(', ', $keys);
-        }
-
-        $this->assertSame([], $missing, implode(' | ', $messages));
+        return $result;
     }
 
+    /**
+     * @return list<string>
+     */
     private function extractTranslationKeys(string $content): array
     {
         $keys = [];