Change record status: 
Project: 
Introduced in branch: 
8.1.x
Introduced in version: 
8.1.0
Description: 

Distributions in Drupal 8 are defined in the info.yml file for the install profile. Additionally to the distribution name and installer theme it is now possible to force the installation to a specific language code as well. Such as if you are doing an install profile for Czech with local currency, payment services, etc. included, you can also force the installation to Czech, so the user does not need to select it at all.

Specify it with the langcode key under the distribution key (in this case in czech.info.yml within the install profile):

name: Czech Drupal
type: profile
description: 'Install with targeted features for Czech users.'
core: 8.x
dependencies:
  - node
  - ....
distribution:
  name: Czech Drupal
  langcode: cz
Impacts: 
Module developers
Updates Done (doc team, etc.)
Online documentation: 
Not done
Theming guide: 
Not done
Module developer documentation: 
Not done
Examples project: 
Not done
Coder Review: 
Not done
Coder Upgrade: 
Not done
Other: 
Other updates done