Η Microsoft language packs have been released MUI - Multilingual User Interface, for Windows 8.1, Windows 8, and Windows 7. These language packs will allow you to apply a new display language to your operating system.
While these are all available through Windows Update or through the Language Control Panel in Windows 8 and above, you may be interested in downloading a language pack so that you can use it when you need it from your hard drive, e.g. to install it on multiple computers at once or if you don't want to download the huge files again after a Windows reinstall.
Here is a huge list of direct links to language packs MUI of Windows 8.1, Windows 8 in the upcoming years, while Windows 7 for Readers of iGuRu.gr.