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					Originally Posted by  quinta@ebf.cz
					 
				 
				It's not particulary important. 2-character language codes just seem more readable to me. 
 
Although... Seems Calibre writes 3-chars into OPF of converted e-books... Isn't _this_ behavior in contrary of EPUB standard? I mean: 
			
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 As far as I know calibre doesn't write a 3-char language code into a converted epub, it writes a 2-char code.
I think it may use a 3-char code (e.g. eng) in its own main database plus the metadata.opf backup file stored with each book record in the calibre library.