The legacy node-copy based content translation module is now removed from core. This module was hidden and impossible to enable on new installs of Drupal 8 for a while.
A new entity field based solution for content translation was added earlier that applies to all content entity types. See https://drupal.org/node/2028009 for that change notice. The application of that to node properties and other entity properties is still ongoing. Of course it needs to get full node property support before it gets feature parity with the node-copy translation module. Those are being tracked in and among other issues.
This change will require a migration path, but given recent changes in core process, this will not be implemented with upgrade hooks. That is being tracked in.