As part of the autocrypt spec, we propose a "backup code" format. This format is designed to contain high entropy, while retaining usability for handling by humans.
An example looks like this:
The idea of a 3 by 3 matrix is to make it easy for the user to keep track of where they are. The blocks of decimals can be easily retained in short term memory and have a low language barrier. Use of this passphrase format is indicated in a header in the ascii armor, to allow display of a specialized input mask. It would be very nice if GnuPG could grow support for this feature.