there are no Group Policy settings to achieve your goal.
The OS language settings are best set at OS installation time, also same for M365 app for enterprise (office 365 proplus).
you can reconfigure Windows language settings using DISM, note that depending on the scenario you may need to supply language files. some tips here https://www.reddit.com/r/sysadmin/comments/6vjdi9/windows_10_default_language_gpo_or_registry_hack/dnuwkk4/
for Office, you'll need to rerun the ODT (setup.exe) with a suitably modified configuration.xml, and will also need to supply the relevant cabfiles, depending on the scenario.