I've noticed there are a few discrepancies in the language codes between 1.5.2 and 2.0. A couple of them are just the 'Name' (which I don't think is important) but a few of the other codes have changed too (French and German for instance) which breaks the language switching.
Rather than list them here, I've uploaded a document I created in Notepad++, noting the changes. Perhaps one of the language experts here could look at it and check what's right and what's wrong.
Download it -
PortableApps.com Locale-2.0 Beta 3