Recently I had a problem with a dev system at a customer site. The system was redeployed from the production site without any problems. Everything worked well, until I tried to customize the system. As soon as I tried to create new attributes or new relationships, the system produced an error

The language code 1033 is not a valid language for this organization

I searched the net, but the only things I found was that this error is listed as an error code of Dynamics CRM (see http://msdn.microsoft.com/en-us/library/bb930493(loband).aspx) and a thread in the Dynamics Forums (http://social.microsoft.com/Forums/en/crm/thread/70bbbf36-1ecb-443e-852a-bebaa70c7206), but sadly without a solution.

After contacting the Dynamics CRM support team, the cause of this error was found in a matter of minutes. The system was redeployed from an installation with German base language to a system with English base language. This is an unsupported scenario.

Neither there was a warning at the redeployment wizard, nor is this mentioned in the Implementation Guide (at least, I haven’t found it there). The support engineer provided me following excerpt there this scenario is described as unsupported

The original deployment and the new deployment of Microsoft Dynamics CRM must be the same base language.

NOTE: Redeployment between different base languages, for example from English to French, is not supported.

To bad that this snippet is only included in the course material for the Installation and Deployment exam and not in the Implementation Guide. The only solution was to do a full reinstall of Dynamics CRM with the same base language as the originating system and to do the reployment again.

Update
In the meantime I got new feedback from the support engineer (thank you José) who is responsible for my case. Microsoft will document this scenario either with a knowledgebase article or by adding the quoted note to the Implementation Guide.