"Language neutral" is not available for content
In Drupal 8 LANGUAGE_NONE (neutral) has changed to LANGUAGE_NOT_SPECIFIED, LANGUAGE_NOT_APPLICABLE and LANGUAGE_MULTIPLE.  

I usually use LANGUAGE_NOT_SPECIFIED where I used to use LANGUAGE_NONE in Drupal 7.

Berdir mentions that all those new options makes no difference to how content is displayed, but they let you treat differently to content on your site if you'd wanted to in views, custom code, ...