Problem
After removing a language that has at least one content translation created, any subsequent attempt to load /admin/content results in the following error:
The website encountered an unexpected error. Please try again later.
Error: Call to a member function getId() on null in Drupal\Core\Entity\Entity\EntityViewDisplay->buildMultiple() (line 254 of core/lib/Drupal/Core/Entity/Entity/EntityViewDisplay.php).Proposed resolution
I don't feel qualified to offer fixes to Drupal core yet but I think the culprit is the statement$view_langcode = $entity->language()->getId();
When you remove a language you get a warning that all translations to that language will be marked as undefined. Well, that statement apparently is trying to getId() of undefined...