We are dealing with a lot of translation and localisation work at the moment and unfortunately there does not seem to be a definitive list of which languages (and their codes) are supported by SharePoint.
So, we reverse engineered the dropdown menu on the SP1 Language pack download page, resulting in the following table.
Chinese (Traditional, Taiwan)
The Locale ID is important for SharePoint Solutions that deploy to the 12/Template/<locale id> folder, for example custom workflow activity .ACTIONS files.
The culture name is used in the names of resource files.