Add translation for new user role

backend/en/user.json

@@ -118,6 +118,7 @@
         "auth_code_invalid": "The authentication code you entered is not valid",
         "2fa_screen_explica": "You have enabled the two-factor authentication option in the user settings. Accordingly, you have just received an access code.<br \/>This code is valid for two hours",
         "access_denied": "Access denied",
-        "user_added_pgp_key": "Updated security settings"
+        "user_added_pgp_key": "Updated security settings",
+        "frontend_only_user": "Special functions of the frontend"
     }
 }