Following up on the introduction of schemas (see http://drupal.org/node/1905070) and configuration overrides (http://drupal.org/node/1928898), the locale system now integrates both. It uses the configuration schema system to identify translatable pieces of shipped configuration such as views, vocabularies, filter formats, email bodies, preconfigured fields, etc. Then it uses the translations imported into the locale module database (which can be automatically downloaded from localize.drupal.org thanks to prior feature additions) to find translations for those configuration pieces and generate configuration override files that the language system will later use to display configuration translated.
From a sitebuilder's point of view, this means all **shipped** configuration (when the .yml file was part of the project package from drupal.org) will be translatable on the site using the built-in interface translation system. (Eventually also on localize.drupal.org thanks to #1933988: Support for Drupal 8 shipped configuration translatables with external dependencies (in effect contrib)).
From a module developer's point of view, this means if you have shipped configuration and use configuration schemas you should use the label and text types in your schemas for translatable pieces of the configuration to participate in this system. If you don't use config schemas, your configuration will just not be translatable.
