A true multi-language ISO supports switching languages post-installation without requiring you to reinstall the OS.

When a user boots from this ISO, the Windows Setup environment detects either the system’s default locale or allows the user to select a preferred language before installation begins. This is the key differentiator: with a multi-language ISO, the entire installation process—from error messages to license agreements—can appear in Hindi, German, Arabic, or Korean without needing to download additional files during setup.

(Deployment Image Servicing and Management) or third-party tools: Microsoft Learn Add languages to Windows Setup - Microsoft Learn

If you need an ISO that comes with multiple languages pre-installed (common for IT deployments), you must "slipstream" them using

For obscure languages (like Welsh or Catalan), you must install them later via as optional features.

If your device meets these specs, the file will install seamlessly.