diff -u b/core/modules/system/system.install b/core/modules/system/system.install
--- b/core/modules/system/system.install
+++ b/core/modules/system/system.install
@@ -1254,6 +1254,10 @@
 function system_update_8004() {
   $database = \Drupal::database();
   $database_schema = $database->schema();
+  $langcode_column_value = [
+    'type => 'varchar_ascii',
+    'length' => 12,
+  ];
 
   $schema = \Drupal::keyValue('entity.storage_schema.sql')->getAll();
   $schema_copy = $schema;
@@ -1266,8 +1270,7 @@
               // Langcode fields have the property 'is_ascii' set, instead
               // they should have set the type to 'varchar_ascii'.
               if ($field_data_property == 'is_ascii') {
-                unset($schema_copy[$item_name][$table_name]['fields'][$field_name]['is_ascii']);
-                $schema_copy[$item_name][$table_name]['fields'][$field_name]['type'] = 'varchar_ascii';
+                $schema_copy[$item_name][$table_name]['fields'][$field_name] = $langcode_column_value;
                 if ($database->driver() == 'mysql') {
                   $database_schema->changeField($table_name, $field_name, $field_name, $schema_copy[$item_name][$table_name]['fields'][$field_name]);
                 }
@@ -1291,8 +1294,7 @@
         $schema_property->setAccessible(TRUE);
         $schema = $schema_property->getValue($field_definition);
         if (isset($schema['columns']['value']['is_ascii'])) {
-          $schema['columns']['value']['type'] = 'varchar_ascii';
-          unset($schema['columns']['value']['is_ascii']);
+          $schema['columns']['value'] = $langcode_column_value;
         }
         $schema_property->setValue($field_definition, $schema);
         $schema_property->setAccessible(FALSE);