If you want to add an extra language pack to your Windows 10 installation, you'll need to follow these additional steps:

Navigate to the folder where you copied the language pack files using the Command Prompt. For example:

Use the DISM tool to install the extra language pack. The command is the same as before:

Download the language pack files ( .cab files) for the extra language you want to add.

Here's the step-by-step guide to offline install a Microsoft Windows 10 language pack: