You need to download the Language Pack CAB file for your desired language.
Download them from the Volume Licensing Service Center (VLSC) https://www.microsoft.com/Licensing/servicecenter/default.aspx. Install these language packs on your SCCM server.
For detailed instructions and troubleshooting steps, refer to the official Microsoft documentation on deploying language packs using SCCM: https://learn.microsoft.com/en-us/troubleshoot/mem/configmgr/app-management/deploy-language-pack