New features

Demo Framework 8.x-2.0-rc7 contains the following updates:

Drush users: Update to Drush 8.1.12+ or higher

Versions of Drush earlier than 8.1.12 will not work with Drupal 8.4.x. Update Drush to 8.1.12 or higher before using it to update to Drupal core 8.4.x or you will encounter fatal errors that prevent updates from running.

Define an internal API and provide a hook for other modules to use to provide their own field details.

Only 1 new, small, feature/bug fix:
Issue #2895585 by StephaneQ: Not all language codes are accepted

This version introduces 'Custom Languages'.
In D7, this module used the 'installed, disabled' core/standard languages. I D8, the Custom languages ware not easily formattable, and each new langugae appears on the site, too. This is not the main usecase of this module. So, you can now create Custom languages, to be used in a 'Language' field.