Change record status: 
Project: 
Introduced in branch: 
8.0.x
Introduced in version: 
8.0.0
Description: 

Drupal 8's configuration system uses the langcode key on each configuration object to store the language that object uses. The system.site langcode value signals what language the site name and slogan are. We used to use this same key to signal what the site default language is. That did not hold in practice. While most cases, these may be the same, they also may not be. So we changed to use a separate key, default_langcode to store the site default language code in the same object.

Before (system.site.yml):

name: Questo è il mio sito
langcode: it

After (system.site.yml):

name: Questo è il mio sito
langcode: it
default_langcode: it

Note that in the after example it is now possible to have the site default different from the langcode of this file.

Impacts: 
Module developers