List of language codes?

[avid-e-reader]

The AmazonKindlePublishingGuidelines.pdf doesn't seem to contain a list of valid language codes.

So what I'd like is documentation about what codes are available, because I convert ebooks in other languages, sometimes.

The language of particular interest today is Cebuano, and it doesn't have an ISO 639-1 code, so I tried the ISO 639-2 code (3 letters: ceb) and got a "Language not recognized in metadata" error.

Not sure where to turn next. I suppose I could lie, but that usually causes confusion later...