diff --git a/models/classes/Platform/Service/Oidc/Lti1p3UserAuthenticator.php b/models/classes/Platform/Service/Oidc/Lti1p3UserAuthenticator.php
index a1d64061..ec4f4f66 100644
--- a/models/classes/Platform/Service/Oidc/Lti1p3UserAuthenticator.php
+++ b/models/classes/Platform/Service/Oidc/Lti1p3UserAuthenticator.php
@@ -69,7 +69,7 @@ private function getUserIdentity(string $userId): UserIdentity
 
         $email = $this->getPropertyValue($user, UserRdf::PROPERTY_MAIL);
 
-        $locale = $this->getPropertyValue($user, UserRdf::PROPERTY_DEFLG);
+        $locale = $this->detectLocale($user);
 
         return new UserIdentity($login, trim($fullName), $email, $firstName, $lastName, null, $locale);
     }
@@ -79,6 +79,18 @@ private function getPropertyValue(User $user, string $propertyName): ?string
         return $user->getPropertyValues($propertyName)[0] ?? null;
     }
 
+    private function detectLocale(User $user): ?string
+    {
+        if (
+            !empty($this->getPropertyValue($user, UserRdf::PROPERTY_LOGIN))
+            || !defined('DEFAULT_ANONYMOUS_INTERFACE_LANG')
+        ) {
+            return $this->getPropertyValue($user, UserRdf::PROPERTY_DEFLG);
+        } else {
+            return DEFAULT_ANONYMOUS_INTERFACE_LANG;
+        }
+    }
+
     private function getUserService(): UserService
     {
         return $this->getServiceLocator()->get(UserService::SERVICE_ID);
diff --git a/test/unit/models/classes/Platform/Service/Oidc/Lti1p3UserAuthenticatorTest.php b/test/unit/models/classes/Platform/Service/Oidc/Lti1p3UserAuthenticatorTest.php
index fab18695..a08a77ac 100644
--- a/test/unit/models/classes/Platform/Service/Oidc/Lti1p3UserAuthenticatorTest.php
+++ b/test/unit/models/classes/Platform/Service/Oidc/Lti1p3UserAuthenticatorTest.php
@@ -106,7 +106,13 @@ public function testAnonymousOrGuestUser(): void
                 new UserIdentity(
                     'userId#123456',
                     '',
-                    ''
+                    '',
+                    null,
+                    null,
+                    null,
+                    defined('DEFAULT_ANONYMOUS_INTERFACE_LANG')
+                        ? DEFAULT_ANONYMOUS_INTERFACE_LANG
+                        : DEFAULT_LANG
                 )
             ),
             $this->subject->authenticate($registration, 'userId#123456')
@@ -132,6 +138,7 @@ private function expectUser(
                 [UserRdf::PROPERTY_FIRSTNAME],
                 [UserRdf::PROPERTY_LASTNAME],
                 [UserRdf::PROPERTY_MAIL],
+                [UserRdf::PROPERTY_LOGIN],
                 [UserRdf::PROPERTY_DEFLG]
             )
             ->willReturnOnConsecutiveCalls(
@@ -139,7 +146,8 @@ private function expectUser(
                 [$firstName],
                 [$lastName],
                 [$email],
-                [$locale],
+                [$login],
+                [$locale]
             );
 
         $this->userService