I got the following error while trying to create a list based on a custom template:
The language is not supported on the server - Office SharePoint Server2007 installation
I came across this post but that did not seem to resolve my problem even after restarting the server.
Comparing other servers in the farm, I noticed that HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Shared Tools\Web Server Extensions\12.0 was actually missing InstalledLanguages.
So I saved the following to a .reg file, double-clicked and voila! It worked like a charm:
Windows Registry Editor Version 5.00
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Shared Tools\Web Server Extensions\12.0\InstalledLanguages]"1033"="12.0.4518.1016"