The new Team Foundation Server Express product is designed to work with the Express version of SQL Server.  It conveniently installs SQL Server Express automatically during configuration on machines where it is not detected.  However, SQL Server and SQL Server Express impose additional restrictions on a system’s language settings that TFS by itself does not normally require in order to support Multilingual User Interface (MUI) systems.  This means that TFS must impose additional blocks for language mismatches when it is installing SQL Server Express.

The basic language restrictions for SQL Server are as follows:

• English SQL Server is supported on all localized versions of the OS.
• Localized versions of SQL Server are supported on the same localized OS or the English OS with MUI enabled for the same language.

 Note that Windows has three different language settings.  If it is configured such that any of these settings do not match, or your setup does not comply with the basic restrictions above, you will get the following error during the readiness checks for TFS Express: 

If you see this error, confirm that the following 3 OS settings match.  This can be done in the Windows Control Panel or by using the Windows API calls listed in the table:

For more information about language requirements for SQL Server and how to change language settings in Windows, visit this blog post:  http://blogs.msdn.com/b/petersad/archive/2010/02/04/install-sql-server-2008-r2-on-a-multilingual-user-interface-mui-system.aspx

We also have more supporting documentation for this topic on the MSDN Library:

Local Language Versions in SQL Server:  http://msdn.microsoft.com/en-us/library/ee210665(SQL.105).aspx

How to Change Operating System Settings to Support Localized Versions of SQL Server:  http://msdn.microsoft.com/en-us/library/ms144258(v=sql.105).aspx