diff --git a/core/modules/language/migrations/d6_language_content_menu_settings.yml b/core/modules/language/migrations/d6_language_content_menu_settings.yml
deleted file mode 100644
index 8e015f21829d058f04ba527b727bb247e2404cfb..0000000000000000000000000000000000000000
--- a/core/modules/language/migrations/d6_language_content_menu_settings.yml
+++ /dev/null
@@ -1,21 +0,0 @@
-id: d6_language_content_menu_settings
-label: Drupal 6 language content menu settings
-migration_tags:
-  - Drupal 6
-  - Configuration
-source:
-  plugin: extension
-  name: i18nmenu
-  constants:
-    target_type: 'menu_link_content'
-    langcode: 'site_default'
-process:
-  target_entity_type_id: 'constants/target_type'
-  # menu_link_content has a bundle key but no bundle support so use the entity
-  # type as the bundle.
-  target_bundle: 'constants/target_type'
-  default_langcode: 'constants/langcode'
-  # Drupal 6 menus are translated when the i18nmenu module is enabled.
-  language_alterable: status
-destination:
-  plugin: entity:language_content_settings
diff --git a/core/modules/language/tests/src/Kernel/Migrate/d6/MigrateLanguageContentMenuSettingsTest.php b/core/modules/language/tests/src/Kernel/Migrate/d6/MigrateLanguageContentMenuSettingsTest.php
deleted file mode 100644
index 0148452dc977428abacb51096875e4835341abdb..0000000000000000000000000000000000000000
--- a/core/modules/language/tests/src/Kernel/Migrate/d6/MigrateLanguageContentMenuSettingsTest.php
+++ /dev/null
@@ -1,68 +0,0 @@
-<?php
-
-namespace Drupal\Tests\language\Kernel\Migrate\d6;
-
-use Drupal\language\Entity\ConfigurableLanguage;
-use Drupal\language\Entity\ContentLanguageSettings;
-use Drupal\Core\Language\LanguageInterface;
-use Drupal\Tests\migrate_drupal\Kernel\d6\MigrateDrupal6TestBase;
-
-/**
- * Tests migration of the ability to translate menu content.
- *
- * @group migrate_drupal_6
- */
-class MigrateLanguageContentMenuSettingsTest extends MigrateDrupal6TestBase {
-
-  /**
-   * {@inheritdoc}
-   */
-  public static $modules = [
-    'language',
-    'content_translation',
-    'menu_link_content',
-  ];
-
-  /**
-   * {@inheritdoc}
-   */
-  protected function setUp() {
-    parent::setUp();
-    // Create some languages.
-    ConfigurableLanguage::createFromLangcode('en')->save();
-    ConfigurableLanguage::createFromLangcode('fr')->save();
-    $this->executeMigrations(['d6_language_content_menu_settings']);
-  }
-
-  /**
-   * Tests migration of menu translation ability.
-   */
-  public function testLanguageMenuContent() {
-    $config = ContentLanguageSettings::load('menu_link_content.menu_link_content');
-    $this->assertInstanceOf(ContentLanguageSettings::class, $config);
-    $this->assertSame('menu_link_content', $config->getTargetEntityTypeId());
-    $this->assertSame('menu_link_content', $config->getTargetBundle());
-    $this->assertSame(LanguageInterface::LANGCODE_SITE_DEFAULT, $config->getDefaultLangcode());
-    $this->assertTrue($config->isLanguageAlterable());
-
-    // Test that menus are not alterable when the i18nmenu is not enabled.
-    $this->sourceDatabase->update('system')
-      ->fields(['status' => 0])
-      ->condition('name', 'i18nmenu')
-      ->execute();
-
-    /** @var \Drupal\migrate\Plugin\MigrationInterface $migration */
-    $migration = $this->getMigration('d6_language_content_menu_settings');
-    // Indicate we're rerunning a migration that's already run.
-    $migration->getIdMap()->prepareUpdate();
-    $this->executeMigration($migration);
-
-    $config = ContentLanguageSettings::load('menu_link_content.menu_link_content');
-    $this->assertInstanceOf(ContentLanguageSettings::class, $config);
-    $this->assertSame('menu_link_content', $config->getTargetEntityTypeId());
-    $this->assertSame('menu_link_content', $config->getTargetBundle());
-    $this->assertSame(LanguageInterface::LANGCODE_SITE_DEFAULT, $config->getDefaultLangcode());
-    $this->assertFalse($config->isLanguageAlterable());
-  }
-
-}
diff --git a/core/modules/menu_link_content/migrations/d6_menu_links_translation.yml b/core/modules/menu_link_content/migrations/d6_menu_links_translation.yml
deleted file mode 100644
index 71e55992e8afe69dc4b309fe43443eefc933637b..0000000000000000000000000000000000000000
--- a/core/modules/menu_link_content/migrations/d6_menu_links_translation.yml
+++ /dev/null
@@ -1,54 +0,0 @@
-id: d6_menu_links_translation
-label: Menu links
-migration_tags:
-  - Drupal 6
-  - Content
-source:
-  plugin: d6_menu_link_translation
-process:
-  id: mlid
-  langcode: language
-  title:
-    -
-      plugin: callback
-      source:
-        - title_translated
-        - link_title
-      callable: array_filter
-    -
-      plugin: callback
-      callable: current
-  description:
-    -
-      plugin: callback
-      source:
-        - description_translated
-        - description
-      callable: array_filter
-    -
-      plugin: callback
-      callable: current
-  menu_name:
-    -
-      plugin: migration_lookup
-      # The menu migration is in the system module.
-      migration: d6_menu
-      source: menu_name
-    -
-      plugin: skip_on_empty
-      method: row
-    -
-      plugin: static_map
-      map:
-        management: admin
-      bypass: true
-destination:
-  plugin: entity:menu_link_content
-  default_bundle: menu_link_content
-  no_stub: true
-  translations: true
-migration_dependencies:
-  required:
-    - language
-    - d6_menu
-    - d6_menu_links
diff --git a/core/modules/menu_link_content/src/Plugin/migrate/source/d6/MenuLinkTranslation.php b/core/modules/menu_link_content/src/Plugin/migrate/source/d6/MenuLinkTranslation.php
deleted file mode 100644
index dbc455b3532114a2f07f4b68e3c4435793aee4f6..0000000000000000000000000000000000000000
--- a/core/modules/menu_link_content/src/Plugin/migrate/source/d6/MenuLinkTranslation.php
+++ /dev/null
@@ -1,97 +0,0 @@
-<?php
-
-namespace Drupal\menu_link_content\Plugin\migrate\source\d6;
-
-use Drupal\migrate\Row;
-use Drupal\menu_link_content\Plugin\migrate\source\MenuLink;
-
-/**
- * Gets Menu link translations from source database.
- *
- * @MigrateSource(
- *   id = "d6_menu_link_translation",
- *   source_module = "i18nmenu"
- * )
- */
-class MenuLinkTranslation extends MenuLink {
-
-  /**
-   * {@inheritdoc}
-   */
-  public function query() {
-    // Ideally, the query would return rows for each language for each menu link
-    // with the translations for both the title and description or just the
-    // title translation or just the description translation. That query quickly
-    // became complex and would be difficult to maintain.
-    // Therefore, build a query based on i18nstrings table where each row has
-    // the translation for only one property, either title or description. The
-    // method prepareRow() is then used to obtain the translation for the other
-    // property.
-    // The query starts with the same query as menu_link.
-    $query = parent::query();
-
-    // Add in the property, which is either title or description.
-    $query->leftJoin('i18n_strings', 'i18n', 'ml.mlid = i18n.objectid');
-    $query->isNotNull('i18n.lid');
-    $query->addField('i18n', 'lid');
-    $query->addField('i18n', 'property');
-
-    // Add in the translation for the property.
-    $query->innerJoin('locales_target', 'lt', 'i18n.lid = lt.lid');
-    $query->addField('lt', 'language');
-    $query->addField('lt', 'translation');
-    return $query;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function prepareRow(Row $row) {
-    $language = $row->getSourceProperty('language');
-    $mlid = $row->getSourceProperty('mlid');
-
-    // If this row has been migrated it is a duplicate then skip it.
-    if ($this->idMap->lookupDestinationIds(['mlid' => $mlid, 'language' => $language])) {
-      return FALSE;
-    }
-
-    // Save the translation for this property.
-    $property = $row->getSourceProperty('property');
-    $row->setSourceProperty($property . '_translated', $row->getSourceProperty('translation'));
-
-    // Get the translation, if one exists, for the property not already in the
-    // row.
-    $other_property = ($property == 'title') ? 'description' : 'title';
-    $query = $this->select('i18n_strings', 'i18n')
-      ->fields('i18n', ['lid'])
-      ->condition('i18n.property', $other_property)
-      ->condition('i18n.objectid', $mlid);
-    $query->leftJoin('locales_target', 'lt', 'i18n.lid = lt.lid');
-    $query->condition('lt.language', $language);
-    $query->addField('lt', 'translation');
-    $results = $query->execute()->fetchAssoc();
-    $row->setSourceProperty($other_property . '_translated', $results['translation']);
-    parent::prepareRow($row);
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function fields() {
-    $fields = [
-      'language' => $this->t('Language for this menu.'),
-      'title_translated' => $this->t('Menu link title translation.'),
-      'description_translated' => $this->t('Menu link description translation.'),
-    ];
-    return parent::fields() + $fields;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function getIds() {
-    $ids['language']['type'] = 'string';
-    return parent::getIds() + $ids;
-  }
-
-}
diff --git a/core/modules/menu_link_content/tests/src/Kernel/Migrate/d6/MigrateMenuLinkTest.php b/core/modules/menu_link_content/tests/src/Kernel/Migrate/d6/MigrateMenuLinkTest.php
index 36e4f30dc0ae4278d99f3eb92e9be12b375e6498..7c7b57fbabbcca2f6fdd11aac4e3e32e7246f1e2 100644
--- a/core/modules/menu_link_content/tests/src/Kernel/Migrate/d6/MigrateMenuLinkTest.php
+++ b/core/modules/menu_link_content/tests/src/Kernel/Migrate/d6/MigrateMenuLinkTest.php
@@ -84,7 +84,7 @@ protected function assertEntity($id, $title, $menu, $description, $enabled, $exp
    * Tests migration of menu links.
    */
   public function testMenuLinks() {
-    $this->assertEntity('138', 'Test 1', 'secondary-links', 'Test menu link 1', TRUE, FALSE, ['attributes' => ['title' => 'Test menu link 1'], 'langcode' => 'en'], 'internal:/user/login', -50);
+    $this->assertEntity('138', 'Test 1', 'secondary-links', 'Test menu link 1', TRUE, FALSE, ['attributes' => ['title' => 'Test menu link 1']], 'internal:/user/login', -50);
     $this->assertEntity('139', 'Test 2', 'secondary-links', 'Test menu link 2', TRUE, TRUE, ['query' => 'foo=bar', 'attributes' => ['title' => 'Test menu link 2']], 'internal:/admin', -49);
     $this->assertEntity('140', 'Drupal.org', 'secondary-links', NULL, TRUE, FALSE, ['attributes' => ['title' => '']], 'https://www.drupal.org', -50);
 
@@ -96,9 +96,6 @@ public function testMenuLinks() {
     $this->assertEntity('460', 'Le Vrai McCoy', 'primary-links', NULL, TRUE, FALSE, ['attributes' => ['title' => ''], 'alter' => TRUE], 'entity:node/10', 0);
     $this->assertEntity('461', 'Abantu zulu', 'primary-links', NULL, TRUE, FALSE, ['attributes' => ['title' => ''], 'alter' => TRUE], 'entity:node/12', 0);
     $this->assertEntity('462', 'The Zulu People', 'primary-links', NULL, TRUE, FALSE, ['attributes' => ['title' => ''], 'alter' => TRUE], 'entity:node/12', 0);
-
-    // Test the migration of menu links translation.
-    $this->assertEntity('463', 'fr - Test 1', 'secondary-links', 'fr - Test menu link 1', TRUE, FALSE, ['attributes' => ['title' => 'fr - Test menu link 1'], 'langcode' => 'fr', 'alter' => TRUE], 'internal:/user/login', -49);
   }
 
 }
diff --git a/core/modules/menu_link_content/tests/src/Kernel/Migrate/d6/MigrateMenuLinkTranslationTest.php b/core/modules/menu_link_content/tests/src/Kernel/Migrate/d6/MigrateMenuLinkTranslationTest.php
deleted file mode 100644
index 21911f06f419038b6a152cda4417fb9b30b07a85..0000000000000000000000000000000000000000
--- a/core/modules/menu_link_content/tests/src/Kernel/Migrate/d6/MigrateMenuLinkTranslationTest.php
+++ /dev/null
@@ -1,93 +0,0 @@
-<?php
-
-namespace Drupal\Tests\menu_link_content\Kernel\Migrate\d6;
-
-use Drupal\menu_link_content\Entity\MenuLinkContent;
-use Drupal\Tests\migrate_drupal\Kernel\d6\MigrateDrupal6TestBase;
-
-/**
- * Menu link migration.
- *
- * @group migrate_drupal_6
- */
-class MigrateMenuLinkTranslationTest extends MigrateDrupal6TestBase {
-
-  /**
-   * {@inheritdoc}
-   */
-  public static $modules = ['menu_ui', 'menu_link_content', 'language'];
-
-  /**
-   * {@inheritdoc}
-   */
-  protected function setUp() {
-    parent::setUp();
-    $this->migrateContent();
-    $this->installSchema('system', ['router']);
-    $this->installEntitySchema('menu_link_content');
-    $this->executeMigrations([
-      'language',
-      'd6_menu',
-      'd6_menu_links',
-      'd6_menu_links_translation',
-    ]);
-  }
-
-  /**
-   * Tests migration of menu links.
-   */
-  public function testMenuLinks() {
-    /** @var \Drupal\menu_link_content\Entity\MenuLinkContent $menu_link */
-    $menu_link = MenuLinkContent::load(139)->getTranslation('fr');
-    $this->assertInstanceOf(MenuLinkContent::class, $menu_link);
-    $this->assertSame('fr - Test 2', $menu_link->getTitle());
-    $this->assertSame('fr - Test menu link 2', $menu_link->getDescription());
-    $this->assertSame('secondary-links', $menu_link->getMenuName());
-    $this->assertTrue($menu_link->isEnabled());
-    $this->assertTrue($menu_link->isExpanded());
-    $this->assertSame(['query' => 'foo=bar', 'attributes' => ['title' => 'Test menu link 2']], $menu_link->link->options);
-    $this->assertSame('internal:/admin', $menu_link->link->uri);
-    $this->assertSame(-49, $menu_link->getWeight());
-
-    $menu_link = MenuLinkContent::load(139)->getTranslation('zu');
-    $this->assertInstanceOf(MenuLinkContent::class, $menu_link);
-    $this->assertSame('Test 2', $menu_link->getTitle());
-    $this->assertSame('zu - Test menu link 2', $menu_link->getDescription());
-    $this->assertSame('secondary-links', $menu_link->getMenuName());
-    $this->assertTrue($menu_link->isEnabled());
-    $this->assertTrue($menu_link->isExpanded());
-    $this->assertSame(['query' => 'foo=bar', 'attributes' => ['title' => 'Test menu link 2']], $menu_link->link->options);
-    $this->assertSame('internal:/admin', $menu_link->link->uri);
-    $this->assertSame(-49, $menu_link->getWeight());
-
-    $menu_link = MenuLinkContent::load(140)->getTranslation('fr');
-    $this->assertInstanceOf(MenuLinkContent::class, $menu_link);
-    $this->assertSame('fr - Drupal.org', $menu_link->getTitle());
-    $this->assertSame('', $menu_link->getDescription());
-    $this->assertSame('secondary-links', $menu_link->getMenuName());
-    $this->assertTrue($menu_link->isEnabled());
-    $this->assertFalse($menu_link->isExpanded());
-    $this->assertSame(['attributes' => ['title' => '']], $menu_link->link->options);
-    $this->assertSame('https://www.drupal.org', $menu_link->link->uri);
-    $this->assertSame(-50, $menu_link->getWeight());
-
-    $menu_link = MenuLinkContent::load(463);
-    $this->assertInstanceOf(MenuLinkContent::class, $menu_link);
-    $this->assertSame('fr - Test 1', $menu_link->getTitle());
-    $this->assertSame('fr - Test menu link 1', $menu_link->getDescription());
-    $this->assertSame('secondary-links', $menu_link->getMenuName());
-    $this->assertTrue($menu_link->isEnabled());
-    $this->assertFalse($menu_link->isExpanded());
-    $attributes = [
-      'attributes' => [
-        'title' => 'fr - Test menu link 1',
-      ],
-      'langcode' => 'fr',
-      'alter' => TRUE,
-    ];
-    $this->assertSame($attributes, $menu_link->link->options);
-    $this->assertSame('internal:/user/login', $menu_link->link->uri);
-    $this->assertSame(-49, $menu_link->getWeight());
-  }
-
-}
diff --git a/core/modules/menu_link_content/tests/src/Kernel/Plugin/migrate/source/d6/MenuLinkTranslationTest.php b/core/modules/menu_link_content/tests/src/Kernel/Plugin/migrate/source/d6/MenuLinkTranslationTest.php
deleted file mode 100644
index d373bb25873cd258fcc927a317a2609062e91ea0..0000000000000000000000000000000000000000
--- a/core/modules/menu_link_content/tests/src/Kernel/Plugin/migrate/source/d6/MenuLinkTranslationTest.php
+++ /dev/null
@@ -1,250 +0,0 @@
-<?php
-
-namespace Drupal\Tests\menu_link_content\Kernel\Plugin\migrate\source\d6;
-
-use Drupal\Tests\migrate\Kernel\MigrateSqlSourceTestBase;
-
-/**
- * Tests menu link translation source plugin.
- *
- * @covers \Drupal\menu_link_content\Plugin\migrate\source\d6\MenuLinkTranslation
- * @group menu_link_content
- */
-class MenuLinkTranslationTest extends MigrateSqlSourceTestBase {
-
-  /**
-   * {@inheritdoc}
-   */
-  public static $modules = ['menu_link_content', 'migrate_drupal'];
-
-  /**
-   * {@inheritdoc}
-   */
-  public function providerSource() {
-    $test = [];
-    $test[0]['source_data']['menu_links'] = [
-      [
-        'menu_name' => 'menu-test-menu',
-        'mlid' => 138,
-        'plid' => 0,
-        'link_path' => 'admin',
-        'router_path' => 'admin',
-        'link_title' => 'Test 1',
-        'options' => 'a:1:{s:10:"attributes";a:1:{s:5:"title";s:16:"Test menu link 1";}}',
-        'module' => 'menu',
-        'hidden' => 0,
-        'external' => 0,
-        'has_children' => 1,
-        'expanded' => 0,
-        'weight' => 15,
-        'depth' => 1,
-        'customized' => 1,
-        'p1' => '138',
-        'p2' => '0',
-        'p3' => '0',
-        'p4' => '0',
-        'p5' => '0',
-        'p6' => '0',
-        'p7' => '0',
-        'p8' => '0',
-        'p9' => '0',
-        'updated' => '0',
-      ],
-      [
-        'menu_name' => 'menu-test-menu',
-        'mlid' => 139,
-        'plid' => 138,
-        'link_path' => 'admin/modules',
-        'router_path' => 'admin/modules',
-        'link_title' => 'Test 2',
-        'options' => 'a:1:{s:10:"attributes";a:1:{s:5:"title";s:16:"Test menu link 2";}}',
-        'module' => 'menu',
-        'hidden' => 0,
-        'external' => 0,
-        'has_children' => 0,
-        'expanded' => 0,
-        'weight' => 12,
-        'depth' => 2,
-        'customized' => 1,
-        'p1' => '138',
-        'p2' => '139',
-        'p3' => '0',
-        'p4' => '0',
-        'p5' => '0',
-        'p6' => '0',
-        'p7' => '0',
-        'p8' => '0',
-        'p9' => '0',
-        'updated' => '0',
-      ],
-      [
-        'menu_name' => 'menu-test-menu',
-        'mlid' => 140,
-        'plid' => 0,
-        'link_path' => 'https://www.drupal.org',
-        'router_path' => 'admin/modules',
-        'link_title' => 'Test 2',
-        'options' => 'a:1:{s:10:"attributes";a:1:{s:5:"title";s:16:"Test menu link 2";}}',
-        'module' => 'menu',
-        'hidden' => 0,
-        'external' => 0,
-        'has_children' => 0,
-        'expanded' => 0,
-        'weight' => 12,
-        'depth' => 2,
-        'customized' => 1,
-        'p1' => '0',
-        'p2' => '0',
-        'p3' => '0',
-        'p4' => '0',
-        'p5' => '0',
-        'p6' => '0',
-        'p7' => '0',
-        'p8' => '0',
-        'p9' => '0',
-        'updated' => '0',
-      ],
-      [
-        'menu_name' => 'menu-test-menu',
-        'mlid' => 141,
-        'plid' => 0,
-        'link_path' => 'https://api.drupal.org/api/drupal/8.3.x',
-        'router_path' => 'admin/modules',
-        'link_title' => 'Test 3',
-        'options' => 'a:1:{s:10:"attributes";a:1:{s:5:"title";s:16:"Test menu link 3";}}',
-        'module' => 'menu',
-        'hidden' => 0,
-        'external' => 0,
-        'has_children' => 0,
-        'expanded' => 0,
-        'weight' => 12,
-        'depth' => 2,
-        'customized' => 1,
-        'p1' => '0',
-        'p2' => '0',
-        'p3' => '0',
-        'p4' => '0',
-        'p5' => '0',
-        'p6' => '0',
-        'p7' => '0',
-        'p8' => '0',
-        'p9' => '0',
-        'updated' => '0',
-      ],
-    ];
-    $test[0]['source_data']['i18n_strings'] = [
-      [
-        'lid' => 1,
-        'objectid' => 139,
-        'type' => 'item',
-        'property' => 'title',
-        'objectindex' => 0,
-        'format' => 0,
-      ],
-      [
-        'lid' => 2,
-        'objectid' => 139,
-        'type' => 'item',
-        'property' => 'description',
-        'objectindex' => 0,
-        'format' => 0,
-      ],
-      [
-        'lid' => 3,
-        'objectid' => 140,
-        'type' => 'item',
-        'property' => 'description',
-        'objectindex' => 0,
-        'format' => 0,
-      ],
-      [
-        'lid' => 4,
-        'objectid' => 141,
-        'type' => 'item',
-        'property' => 'title',
-        'objectindex' => 0,
-        'format' => 0,
-      ],
-    ];
-    $test[0]['source_data']['locales_target'] = [
-      [
-        'lid' => 1,
-        'language' => 'fr',
-        'translation' => 'fr - title translation',
-        'plid' => 0,
-        'plural' => 0,
-        'i18n_status' => 0,
-      ],
-      [
-        'lid' => 2,
-        'language' => 'fr',
-        'translation' => 'fr - description translation',
-        'plid' => 0,
-        'plural' => 0,
-        'i18n_status' => 0,
-      ],
-      [
-        'lid' => 3,
-        'language' => 'zu',
-        'translation' => 'zu - description translation',
-        'plid' => 0,
-        'plural' => 0,
-        'i18n_status' => 0,
-      ],
-      [
-        'lid' => 4,
-        'language' => 'zu',
-        'translation' => 'zu - title translation',
-        'plid' => 0,
-        'plural' => 0,
-        'i18n_status' => 0,
-      ],
-    ];
-
-    $test[0]['expected_results'] = [
-      [
-        'menu_name' => 'menu-test-menu',
-        'mlid' => 139,
-        'property' => 'title',
-        'language' => 'fr',
-        'link_title' => 'Test 2',
-        'description' => 'Test menu link 2',
-        'title_translated' => 'fr - title translation',
-        'description_translated' => 'fr - description translation',
-      ],
-      [
-        'menu_name' => 'menu-test-menu',
-        'mlid' => 139,
-        'property' => 'description',
-        'language' => 'fr',
-        'link_title' => 'Test 2',
-        'description' => 'Test menu link 2',
-        'title_translated' => 'fr - title translation',
-        'description_translated' => 'fr - description translation',
-      ],
-      [
-        'menu_name' => 'menu-test-menu',
-        'mlid' => 140,
-        'property' => 'description',
-        'language' => 'zu',
-        'link_title' => 'Test 2',
-        'description' => 'Test menu link 2',
-        'title_translated' => NULL,
-        'description_translated' => 'zu - description translation',
-      ],
-      [
-        'menu_name' => 'menu-test-menu',
-        'mlid' => 141,
-        'property' => 'title',
-        'language' => 'zu',
-        'link_title' => 'Test 3',
-        'description' => 'Test menu link 3',
-        'title_translated' => 'zu - title translation',
-        'description_translated' => NULL,
-      ],
-    ];
-
-    return $test;
-  }
-
-}
diff --git a/core/modules/migrate/src/Plugin/migrate/id_map/Sql.php b/core/modules/migrate/src/Plugin/migrate/id_map/Sql.php
index 946b208a101a1c0d696c6d1f440751b514efa66b..a69e31cba9d58cfe8e86b5a44749fb757f229f97 100644
--- a/core/modules/migrate/src/Plugin/migrate/id_map/Sql.php
+++ b/core/modules/migrate/src/Plugin/migrate/id_map/Sql.php
@@ -563,13 +563,9 @@ public function lookupDestinationIds(array $source_id_values) {
     $conditions = [];
     foreach ($this->sourceIdFields() as $field_name => $db_field) {
       if ($is_associative) {
-        // Ensure to handle array elements with a NULL value.
-        if (array_key_exists($field_name, $source_id_values)) {
-          // Associative $source_id_values can have fields out of order.
-          if (isset($source_id_values[$field_name])) {
-            // Only add a condition if the value is not NULL.
-            $conditions[$db_field] = $source_id_values[$field_name];
-          }
+        // Associative $source_id_values can have fields out of order.
+        if (isset($source_id_values[$field_name])) {
+          $conditions[$db_field] = $source_id_values[$field_name];
           unset($source_id_values[$field_name]);
         }
       }
@@ -584,8 +580,7 @@ public function lookupDestinationIds(array $source_id_values) {
     }
 
     if (!empty($source_id_values)) {
-      $var_dump = var_export($source_id_values, TRUE);
-      throw new MigrateException(sprintf("Extra unknown items in source IDs: %s", $var_dump));
+      throw new MigrateException("Extra unknown items in source IDs");
     }
 
     $query = $this->getDatabase()->select($this->mapTableName(), 'map')
diff --git a/core/modules/migrate/tests/src/Unit/MigrateSqlIdMapTest.php b/core/modules/migrate/tests/src/Unit/MigrateSqlIdMapTest.php
index 001e14c74c8ef4edddb6194d7d846cf06dc0e759..bc849916d7e246cb37d66f42936302b924747875 100644
--- a/core/modules/migrate/tests/src/Unit/MigrateSqlIdMapTest.php
+++ b/core/modules/migrate/tests/src/Unit/MigrateSqlIdMapTest.php
@@ -517,8 +517,6 @@ public function testLookupDestinationIds() {
     $this->assertEquals([[101, 'en'], [101, 'fr'], [101, 'de']], $id_map->lookupDestinationIds(['nid' => 1]));
     $this->assertEquals([[102, 'en']], $id_map->lookupDestinationIds(['nid' => 2]));
     $this->assertEquals([], $id_map->lookupDestinationIds(['nid' => 99]));
-    $this->assertEquals([[101, 'en'], [101, 'fr'], [101, 'de']], $id_map->lookupDestinationIds(['nid' => 1, 'language' => NULL]));
-    $this->assertEquals([[102, 'en']], $id_map->lookupDestinationIds(['nid' => 2, 'language' => NULL]));
     // Out-of-order partial associative list.
     $this->assertEquals([[101, 'en'], [102, 'en']], $id_map->lookupDestinationIds(['language' => 'en']));
     $this->assertEquals([[101, 'fr']], $id_map->lookupDestinationIds(['language' => 'fr']));
@@ -529,14 +527,14 @@ public function testLookupDestinationIds() {
       $this->fail('Too many source IDs should throw');
     }
     catch (MigrateException $e) {
-      $this->assertEquals("Extra unknown items in source IDs: array (\n  0 => 3,\n)", $e->getMessage());
+      $this->assertEquals("Extra unknown items in source IDs", $e->getMessage());
     }
     try {
       $id_map->lookupDestinationIds(['nid' => 1, 'aaa' => '2']);
       $this->fail('Unknown source ID key should throw');
     }
     catch (MigrateException $e) {
-      $this->assertEquals("Extra unknown items in source IDs: array (\n  'aaa' => '2',\n)", $e->getMessage());
+      $this->assertEquals("Extra unknown items in source IDs", $e->getMessage());
     }
 
     // Verify that we are looking up by source_id_hash when all source IDs are
diff --git a/core/modules/migrate_drupal/tests/fixtures/drupal6.php b/core/modules/migrate_drupal/tests/fixtures/drupal6.php
index 4d4e18be489a55017b2d97d465794ae4bae58d16..ea4eee69b2a5b8b032dca59a96f41bc60109d9f9 100644
--- a/core/modules/migrate_drupal/tests/fixtures/drupal6.php
+++ b/core/modules/migrate_drupal/tests/fixtures/drupal6.php
@@ -9710,38 +9710,6 @@
   'objectindex' => '7',
   'format' => '0',
 ))
-->values(array(
-  'lid' => '1674',
-  'objectid' => '463',
-  'type' => 'item',
-  'property' => 'title',
-  'objectindex' => '463',
-  'format' => '0',
-))
-->values(array(
-  'lid' => '1675',
-  'objectid' => '463',
-  'type' => 'item',
-  'property' => 'description',
-  'objectindex' => '463',
-  'format' => '0',
-))
-->values(array(
-  'lid' => '1676',
-  'objectid' => '138',
-  'type' => 'item',
-  'property' => 'title',
-  'objectindex' => '138',
-  'format' => '0',
-))
-->values(array(
-  'lid' => '1677',
-  'objectid' => '138',
-  'type' => 'item',
-  'property' => 'description',
-  'objectindex' => '138',
-  'format' => '0',
-))
 ->execute();
 
 $connection->schema()->createTable('i18n_variable', array(
@@ -22208,34 +22176,6 @@
   'source' => 'Forums',
   'version' => '1',
 ))
-->values(array(
-  'lid' => '1674',
-  'location' => 'item:463:title',
-  'textgroup' => 'menu',
-  'source' => 'fr - Test 1',
-  'version' => '1',
-))
-->values(array(
-  'lid' => '1675',
-  'location' => 'item:463:description',
-  'textgroup' => 'menu',
-  'source' => 'fr - Test menu link 1',
-  'version' => '1',
-))
-->values(array(
-  'lid' => '1676',
-  'location' => 'item:138:title',
-  'textgroup' => 'menu',
-  'source' => 'Test 1',
-  'version' => '1',
-))
-->values(array(
-  'lid' => '1677',
-  'location' => 'item:138:description',
-  'textgroup' => 'menu',
-  'source' => 'Test menu link 1',
-  'version' => '1',
-))
 ->execute();
 
 $connection->schema()->createTable('locales_target', array(
@@ -27765,7 +27705,7 @@
   'link_path' => 'user/login',
   'router_path' => 'user/login',
   'link_title' => 'Test 1',
-  'options' => 'a:2:{s:10:"attributes";a:1:{s:5:"title";s:16:"Test menu link 1";}s:8:"langcode";s:2:"en";}',
+  'options' => 'a:1:{s:10:"attributes";a:1:{s:5:"title";s:16:"Test menu link 1";}}',
   'module' => 'menu',
   'hidden' => '0',
   'external' => '0',
@@ -33887,33 +33827,6 @@
   'p9' => '0',
   'updated' => '0',
 ))
-->values(array(
-  'menu_name' => 'secondary-links',
-  'mlid' => '463',
-  'plid' => '139',
-  'link_path' => 'user/login',
-  'router_path' => 'user/login',
-  'link_title' => 'fr - Test 1',
-  'options' => 'a:3:{s:10:"attributes";a:1:{s:5:"title";s:21:"fr - Test menu link 1";}s:8:"langcode";s:2:"fr";s:5:"alter";b:1;}',
-  'module' => 'menu',
-  'hidden' => '0',
-  'external' => '0',
-  'has_children' => '0',
-  'expanded' => '0',
-  'weight' => '-49',
-  'depth' => '2',
-  'customized' => '1',
-  'p1' => '139',
-  'p2' => '459',
-  'p3' => '0',
-  'p4' => '0',
-  'p5' => '0',
-  'p6' => '0',
-  'p7' => '0',
-  'p8' => '0',
-  'p9' => '0',
-  'updated' => '0',
-))
 ->execute();
 
 $connection->schema()->createTable('menu_router', array(
diff --git a/core/modules/migrate_drupal_ui/tests/src/Functional/d6/MigrateUpgrade6ReviewPageTest.php b/core/modules/migrate_drupal_ui/tests/src/Functional/d6/MigrateUpgrade6ReviewPageTest.php
index 798f0290d84ad47bd3ed9ccd41a054ec000b0d1a..a526de77e95fdc54abd400c8e15edda3e42b5727 100644
--- a/core/modules/migrate_drupal_ui/tests/src/Functional/d6/MigrateUpgrade6ReviewPageTest.php
+++ b/core/modules/migrate_drupal_ui/tests/src/Functional/d6/MigrateUpgrade6ReviewPageTest.php
@@ -89,7 +89,6 @@ protected function getAvailablePaths() {
       'filefield_meta',
       'help',
       'i18n',
-      'i18nmenu',
       'i18nstrings',
       'imageapi',
       'imageapi_gd',
@@ -124,6 +123,7 @@ protected function getMissingPaths() {
       'i18nblocks',
       'i18ncck',
       'i18ncontent',
+      'i18nmenu',
       'i18npoll',
       'i18nprofile',
       'i18nsync',
diff --git a/core/modules/migrate_drupal_ui/tests/src/Functional/d6/MigrateUpgrade6Test.php b/core/modules/migrate_drupal_ui/tests/src/Functional/d6/MigrateUpgrade6Test.php
index f32e60a61057506de77ec6a8cc7fdf0abb1a8833..841b27c310e7b437823d891d8cc0eebb367ad2a7 100644
--- a/core/modules/migrate_drupal_ui/tests/src/Functional/d6/MigrateUpgrade6Test.php
+++ b/core/modules/migrate_drupal_ui/tests/src/Functional/d6/MigrateUpgrade6Test.php
@@ -68,7 +68,7 @@ protected function getEntityCounts() {
       'file' => 8,
       'filter_format' => 7,
       'image_style' => 5,
-      'language_content_settings' => 3,
+      'language_content_settings' => 2,
       'migration' => 105,
       'node' => 17,
       // The 'book' module provides the 'book' node type, and the migration
@@ -85,7 +85,7 @@ protected function getEntityCounts() {
       'tour' => 4,
       'user' => 7,
       'user_role' => 6,
-      'menu_link_content' => 10,
+      'menu_link_content' => 9,
       'view' => 16,
       'date_format' => 11,
       'entity_form_display' => 29,
@@ -106,7 +106,7 @@ protected function getEntityCountsIncremental() {
     $counts['entity_view_display'] = 53;
     $counts['entity_view_mode'] = 14;
     $counts['file'] = 9;
-    $counts['menu_link_content'] = 11;
+    $counts['menu_link_content'] = 10;
     $counts['node'] = 18;
     $counts['taxonomy_term'] = 9;
     $counts['user'] = 8;
@@ -131,7 +131,6 @@ protected function getAvailablePaths() {
       'filefield',
       'filter',
       'forum',
-      'i18nmenu',
       'i18ntaxonomy',
       'imagecache',
       'imagefield',
@@ -176,6 +175,7 @@ protected function getMissingPaths() {
       'i18nblocks',
       'i18ncck',
       'i18ncontent',
+      'i18nmenu',
       // This module is in the missing path list because it is installed on the
       // source site but it is not installed on the destination site.
       'i18nprofile',
diff --git a/core/modules/system/src/Plugin/migrate/source/Extension.php b/core/modules/system/src/Plugin/migrate/source/Extension.php
deleted file mode 100644
index 379939110d070dac56e3dfa1d061921b87e4496b..0000000000000000000000000000000000000000
--- a/core/modules/system/src/Plugin/migrate/source/Extension.php
+++ /dev/null
@@ -1,66 +0,0 @@
-<?php
-
-namespace Drupal\system\Plugin\migrate\source;
-
-use Drupal\migrate\Row;
-use Drupal\migrate_drupal\Plugin\migrate\source\DrupalSqlBase;
-
-/**
- * Gets system data for a legacy extension.
- *
- * @MigrateSource(
- *   id = "extension",
- *   source_module = "system"
- * )
- */
-class Extension extends DrupalSqlBase {
-
-  /**
-   * {@inheritdoc}
-   */
-  public function query() {
-    $query = $this->select('system', 's')
-      ->fields('s');
-
-    if (isset($this->configuration['name'])) {
-      $query->condition('name', (array) $this->configuration['name'], 'IN');
-    }
-    return $query;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function fields() {
-    $fields = [
-      'filename' => $this->t('Filename'),
-      'name' => $this->t('Name'),
-      'type' => $this->t('Type'),
-      'owner' => $this->t('Owner'),
-      'status' => $this->t('Status'),
-      'throttle' => $this->t('Throttle'),
-      'bootstrap' => $this->t('Bootstrap'),
-      'schema_version' => $this->t('Schema version'),
-      'weight' => $this->t('Weight'),
-      'info' => $this->t('Information array'),
-    ];
-    return $fields;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function prepareRow(Row $row) {
-    $row->setSourceProperty('info', unserialize($row->getSourceProperty('info')));
-    return parent::prepareRow($row);
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function getIds() {
-    $ids['name']['type'] = 'string';
-    return $ids;
-  }
-
-}
diff --git a/core/modules/system/tests/src/Kernel/Plugin/migrate/source/ExtensionTest.php b/core/modules/system/tests/src/Kernel/Plugin/migrate/source/ExtensionTest.php
deleted file mode 100644
index c6576019a760d57080b28f32db5c045ac3fc8c5b..0000000000000000000000000000000000000000
--- a/core/modules/system/tests/src/Kernel/Plugin/migrate/source/ExtensionTest.php
+++ /dev/null
@@ -1,77 +0,0 @@
-<?php
-
-namespace Drupal\Tests\system\Kernel\Plugin\migrate\source;
-
-use Drupal\Tests\migrate\Kernel\MigrateSqlSourceTestBase;
-
-/**
- * Tests legacy extension source plugin.
- *
- * @covers \Drupal\system\Plugin\migrate\source\Extension
- * @group migrate_drupal
- */
-class ExtensionTest extends MigrateSqlSourceTestBase {
-
-  /**
-   * {@inheritdoc}
-   */
-  public static $modules = ['system', 'migrate_drupal'];
-
-  /**
-   * {@inheritdoc}
-   */
-  public function providerSource() {
-    $test = [];
-
-    $test[0]['source_data']['system'] = [
-      [
-        'filename' => 'sites/all/modules/i18n/i18nmenu/i18nmenu.module',
-        'name' => 'i18nmenu',
-        'type' => 'module',
-        'owner' => '',
-        'status' => '1',
-        'throttle' => '0',
-        'bootstrap' => '0',
-        'schema_version' => '0',
-        'weight' => '0',
-        'info' => 'a:10:{s:4:"name";s:16:"Menu translation";s:11:"description";s:40:"Supports translatable custom menu items.";s:12:"dependencies";a:4:{i:0;s:4:"i18n";i:1;s:4:"menu";i:2;s:10:"i18nblocks";i:3;s:11:"i18nstrings";}s:7:"package";s:13:"Multilanguage";s:4:"core";s:3:"6.x";s:7:"version";s:8:"6.x-1.10";s:7:"project";s:4:"i18n";s:9:"datestamp";s:10:"1318336004";s:10:"dependents";a:0:{}s:3:"php";s:5:"4.3.5";},',
-      ],
-      [
-        'filename' => 'sites/all/modules/variable/variable.module ',
-        'name' => 'variable',
-        'type' => 'module',
-        'owner' => '',
-        'status' => '1',
-        'throttle' => '0',
-        'bootstrap' => '0',
-        'schema_version' => '-1',
-        'weight' => '0',
-        'info' => 'a:9:{s:4:"name";s:12:"Variable API";s:11:"description";s:12:"Variable API";s:4:"core";s:3:"6.x";s:7:"version";s:14:"6.x-1.0-alpha1";s:7:"project";s:8:"variable";s:9:"datestamp";s:10:"1414059742";s:12:"dependencies";a:0:{}s:10:"dependents";a:0:{}s:3:"php";s:5:"4.3.5";}',
-      ],
-    ];
-
-    $info = unserialize('a:9:{s:4:"name";s:12:"Variable API";s:11:"description";s:12:"Variable API";s:4:"core";s:3:"6.x";s:7:"version";s:14:"6.x-1.0-alpha1";s:7:"project";s:8:"variable";s:9:"datestamp";s:10:"1414059742";s:12:"dependencies";a:0:{}s:10:"dependents";a:0:{}s:3:"php";s:5:"4.3.5";}');
-    $test[0]['expected_results'] = [
-      [
-        'filename' => 'sites/all/modules/variable/variable.module ',
-        'name' => 'variable',
-        'type' => 'module',
-        'owner' => '',
-        'status' => '1',
-        'throttle' => '0',
-        'bootstrap' => '0',
-        'schema_version' => '-1',
-        'weight' => '0',
-        'info' => $info,
-      ],
-    ];
-
-    $test[0]['expected_count'] = NULL;
-    $test[0]['configuration'] = [
-      'name' => 'variable',
-    ];
-
-    return $test;
-  }
-
-}