Iz Windows Help and Support:
How do I get additional display languages?
You can add display languages by installing additional language files. When you install language files, you can view wizards, dialog boxes, menus, Help topics, and other items in Windows in a different language.
There are two types of language files:
Windows 7 Multilingual User Interface Pack (MUI).‌ Windows 7 MUIs provide a translated version of most of the user interface. MUIs require a license to be used and are only available in Windows 7 Ultimate and Windows 7 Enterprise. If you are using Windows 7 Enterprise, contact your system administrator for information about installing additional languages.
To get additional MUIs by using Windows Update
MUIs are available through Windows Update as optional updates. They aren't installed automatically.
Click to open Windows Update.
In the left pane, click Check for updates, and then wait while Windows looks for the latest updates for your computer.
If any updates are found, click Select optional updates.
Select the MUI that you want, and then click OK.
Click Install updates. If you're prompted for an administrator password or confirmation, type the password or provide confirmation.
Note
If Windows doesn't find any updates when you click Check for updates, wait a day and then try again.
Windows 7 Language Interface Pack (LIP).‌ Windows 7 LIPs provide a translated version of the most widely used areas of the user interface. LIPs are freely available to download. Because not all of the user interface is translated, LIPs require at least one parent language. The parts of the user interface that aren't translated into the LIP language are displayed in the parent language. When you download the LIP, you get the parent language requirements for that language. The parent language pack needs to be installed before the LIP can be installed. For more information, including a list of languages available for downloading, go to the Microsoft Local Language Program website.
Note
MUIs and LIPs will work only in a genuine copy of Windows 7. For more information, see What is genuine Windows?
Žal slovenskega LIP ni
http://www.microsoft.com/unlimitedpotential/programs/llp.mspx
here type a patch to Language pack)