With the CurrentUICulture property of the current thread set to a neutral culture like 'de', attempting edit the content in a MOSS Content Editor Web Part results in the following exception:
Server Error in '/' Application.
Culture 'de' is a neutral culture. It cannot be used in formatting and parsing and therefore cannot be set as the thread's current culture.
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.
Exception Details: System.NotSupportedException: Culture 'de' is a neutral culture. It cannot be used in formatting and parsing and therefore cannot be set as the thr...Very boring. On a hunch, I think you can probably get around this by using a specific culture but that may not be possible in very case. This was only an issue while in edit mode, for us, so I got around it by simply setting the CurrenUICulture as en-US whenever a page is in edit mode. Kind of a cheat but our content editors are all English so it doesn't matter.