The .cab extension indicates it is a Cabinet file, a compressed archive used by Windows to store and install system components.
Without this package, a Windows machine can display Chinese characters (if fonts are present) but cannot:
dism /Online /Add-Package /PackagePath:"C:\Temp\Microsoft-Windows-LanguageFeatures-Basic-zh-cn-Package~31bf3856ad364e35~amd64~~.cab"
For a (online mode):