diff -u b/core/modules/content_translation/content_translation.admin.inc b/core/modules/content_translation/content_translation.admin.inc
--- b/core/modules/content_translation/content_translation.admin.inc
+++ b/core/modules/content_translation/content_translation.admin.inc
@@ -111,16 +111,12 @@
                 '#default_value' => $definition->isTranslatable(),
               );
               // Display the column translatability configuration widget.
-              // @todo Remove this special casing when arbitrary settings can be
-              //   stored for any field. See https://drupal.org/node/2224761.
-              if ($definition instanceof FieldInstanceConfigInterface) {
-                $column_element = content_translation_field_sync_widget($definition);
-                if ($column_element) {
-                  $form['settings'][$entity_type_id][$bundle]['columns'][$field_name] = $column_element;
-                  // @todo This should not concern only files.
-                  if (isset($column_element['#options']['file'])) {
-                    $dependent_options_settings["settings[{$entity_type_id}][{$bundle}][columns][{$field_name}]"] = array('file');
-                  }
+              $column_element = content_translation_field_sync_widget($definition);
+              if ($column_element) {
+                $form['settings'][$entity_type_id][$bundle]['columns'][$field_name] = $column_element;
+                // @todo This should not concern only files.
+                if (isset($column_element['#options']['file'])) {
+                  $dependent_options_settings["settings[{$entity_type_id}][{$bundle}][columns][{$field_name}]"] = array('file');
                 }
               }
             }
diff -u b/core/modules/field_ui/src/Form/FieldInstanceEditForm.php b/core/modules/field_ui/src/Form/FieldInstanceEditForm.php
--- b/core/modules/field_ui/src/Form/FieldInstanceEditForm.php
+++ b/core/modules/field_ui/src/Form/FieldInstanceEditForm.php
@@ -134,9 +134,12 @@
       '#weight' => -5,
     );
 
-    // Add instance settings for the field type.
+    // Add instance settings for the field type and a container for third party
+    // settings that modules can add to via hook_form_FORM_ID_alter().
     $form['instance']['settings'] = $items[0]->instanceSettingsForm($form, $form_state);
     $form['instance']['settings']['#weight'] = 10;
+    $form['instance']['third_party_settings'] = array();
+    $form['instance']['third_party_settings']['#weight'] = 11;
 
     // Add handling for default value.
     if ($element = $items->defaultValuesForm($form, $form_state)) {