Hello
Where did you get the language package?
As far as I know, the language for Windows 10 is not available publicly for official website except downloading with Microsoft Account(with Microsoft License argreement).
If you have the License agreement account and the language package is downloaded from official internal website(Fod language package), please check whether there is any package named Microsoft-Windows-Client-LanguagePack-Package. Try to add this package to the installed path then check.
If there is not official method to get the language package, it is recommended to install the package with internet connected directly from the package UI.