Languages are now stored in configuration, langcode property changed to id

Languages used to be stored and maintained in the database. Deploying new languages or translating language names to other languages was not possible. In Drupal 8, languages are now stored with the configuration system.

The most important immediate change for Drupal 8 is that languages are now created with the language code / machine name universally named "id" like any other configuration entity. Prior to this change in Drupal 8:

use Drupal\language\Language;
$language = new Language('langcode' => 'de');
$langcode = $language->langcode;

After this change in Drupal 8:

use Drupal\language\Language;
$language = new Language('id' => 'de');
$langcode = $language->id;