Specify a null value for languages/publisher - it gets reset to the default. (english, published 0101-01-01T00:00:00+00:00)
It makes no sense to have a book
without a language, or one that was never published (or at least written). Or so I would assume.
identifiers -- you need to clear each identifier (as stated in the --help).
Code:
ebook-meta /path/to/ebook --identifier "identifier-type:"
Copyright -- what copyright tag?