The first wave of languages (English, German, French, Spanish, and Japanese) was made available in May 2009, on Windows Update at that time. Today, Microsoft is releasing the remaining languages for Windows Vista and Windows Server 2008 SP2 to Windows Update.
For more information, including languages, on Windows Vista and Windows Server 2008 SP2 click here.
If you have Windows Update configured to download updates automatically, Windows Update will notify you when Windows Vista SP2 and Windows Server 2008 SP2 is ready to be installed.
Source : The Windows Blog.