Once you have the files—whether from a mounted ISO or a downloaded CAB file—you cannot simply double-click them to install. You must use
You downloaded a language pack for Windows 10 or the wrong Windows 11 build (e.g., 24H2 pack on 23H2). Fix: Run winver on your target PC. Look at the Version (e.g., 23H2, OS Build 22621). Download the pack matching that exact Build number. Windows 11 Language Pack Download Offline
A .cab file saved to your computer.