Multi-language support is native in Windows 7 Enterprise and Ultimate editions, but, following this tutorial you be able to alternate entire many languages in Professional and Home Premium editions.
First you’ll need of Vistalizator. This application enable to install muti-language support in all Windows 7 editions and, how it’s portable, you don’t need install it. Download it clicking here.
Now run the Vistalizator and click in “Add languages”.
Browse for language file that you desire and click in “Open”.
Will be show the message below, then click in OK to proceed
A new window will be open with language data and your description, then click in “Install Language”.
Wait the installation process be done.
Now, the Vistalizator will show for you the languages installed in your machine and there will be the recently installed language.
Reboot Windows and voilá. 😉
Now you have Windows 7 Professional/Home Premium with multi-language support.
The only bad thing that I noticed was: all time that you want to change the language, you must to use the Vistalizator, because the Windows 7 Professional and Home Premium doesn’t support this feature natively.