Issue:

Setup failure SQL Server 2008 R2 with the following error message “Invalid Product Key” after specifying a
valid product key is caused by specific language regional settings of the German Operating System. In detail concerns this the format of the “Region and
Language” settings in Control Panel. When the format is set to ‘Deutsch (Österreich)’ or ‘Deutsch (Schweiz)’ setup is failing with the error.

At that stage the SQL Server setup expects that the “Region and Language” would have the format ‘Deutsch (Deutsch)’.

Solution:

Installation runs successfully by changing the format in the Control Panel
->“Region and Language” settings before the installation to ‘Deutsch
(Deutsch)’. After successful installation you can set format  back .

 

In Books Online of SQL Server documented you find the supportrelations between OS and SQL Server language Version.

http://msdn.microsoft.com/en-us/library/ee210665(v=SQL.105).aspx

Snip:

Cross-Language Support


  • The English-language version of SQL Server is supported on all localized versions of operating systems.

  • Localized versions of SQL Server are supported on localized operating systems with the corresponding language or on English-language versions of supported operating systems by using the Windows Multilingual User Interface Pack (MUI) settings. For more information, see How to: Change Operating System Settings to Support Localized Versions.

  • Localized versions of SQL Server can only be upgraded to localized versions of the same language, and cannot be upgraded to the English-language version.

  • Localized versions of SQL Server can also be installed side by side with English-language instances of SQL Server.