It's not free to download but you can usually find it in your own computer - C:\Windows\Service Pack Files\i386\lang. Are you having problems changing from one language to another?
I've bought a used computer which unfortunately doesn't have 'Chinese' in the 'Regional and Language' and I need to read Chinese on my pc. I'm asked to insert a cd rom but I don't have it. i386 is the thing needed for adding a language.