Use the offlineServicing pass to apply unattended Setup settings to an offline Windows image. During this configuration pass, you can add language packs, updates, or other packages to the offline image.
The offlineServicing pass runs during Windows Setup. Setup extracts and installs the Windows image, and then executes Package Manager (Pkgmgr.exe). Packages listed in the servicing section of the answer file are applied to the offline Windows image. The Unattend.xml settings in the offlineServicing pass are applied to the offline Windows image.
Additionally, you can use Package Manager with an answer file to install packages.