Language change while upgrading

Installed: WIN10 Pro 64, U.S. English:
When, via RUFUS methods, upgrading to Win 11, 24H2, (or, not RUFUS... Lenovo ThinkStation P520 has TPM 2.0 in BIOS)
Can the OS language be changed to Polish?
would like to upgrade machine I will be selling from original, valid Win 10 Pro to Win 11 Pro.
thanks for any useful information.
John

No, you can't change the base language of an installed Windows, via upgrade. You can always add new Language Packs to an existing system.

If you needed Polish to be system's language, then find a copy of the Polish 24H2 ISO and do a clean install. Users can have more languages available to them, but you can't switch the base language of an ISO or an already installed Windows. That's always been the rule.

There are specific resource files underlying Windows at the lowest level, and they can't be swapped out. Which is why a clean re-install is required to change the base language.