"The language is not supported on the server. "

If you, like me had the chance of re-installing SharePoint (with all the language packs that you might have used before), it is likely that you have encountered this message.

You will most likely see this message when running the configuration wizard , or attempting to create new sites, even in other languages than the installation.

To sort this issue check if the following registry key is present:

HKLM\SOFTWARE\Microsoft\Shared Tools\Web Server Extensions\12.0\ServerLanguage

If it’s not there create it. Add a new String value:

Key name:  1033

Value =””” (empty)

Reference:

http://blogs.technet.com/stefan_gossner/archive/2006/07/11/441127.aspx