diff -u b/core/modules/comment/src/Plugin/migrate/destination/EntityComment.php b/core/modules/comment/src/Plugin/migrate/destination/EntityComment.php
--- b/core/modules/comment/src/Plugin/migrate/destination/EntityComment.php
+++ b/core/modules/comment/src/Plugin/migrate/destination/EntityComment.php
@@ -42,9 +42,11 @@
   protected $stubCommentedEntityIds;
 
   /**
+   * The language mangager.
+   *
    * @var \Drupal\Core\Language\LanguageManagerInterface
    */
-  protected $language_manager;
+  protected $languageManager;
 
   /**
    * Builds an comment entity destination.
@@ -76,7 +78,7 @@
     parent::__construct($configuration, $plugin_id, $plugin_definition, $migration, $storage, $bundles, $language_manager, $entity_manager, $field_type_manager);
     $this->state = $state;
     $this->entityQuery = $entity_query;
-    $this->language_manager = $language_manager;
+    $this->languageManager = $language_manager;
   }
 
   /**
@@ -90,8 +92,7 @@
       $plugin_definition,
       $migration,
       $container->get('entity.manager')->getStorage($entity_type),
-      array_keys($container->get('entity.manager')
-        ->getBundleInfo($entity_type)),
+      array_keys($container->get('entity.manager')->getBundleInfo($entity_type)),
       $container->get('language_manager'),
       $container->get('entity.manager'),
       $container->get('plugin.manager.field.field_type'),
diff -u b/core/modules/config_translation/src/Plugin/migrate/source/d6/I18nBlock.php b/core/modules/config_translation/src/Plugin/migrate/source/d6/I18nBlock.php
--- b/core/modules/config_translation/src/Plugin/migrate/source/d6/I18nBlock.php
+++ b/core/modules/config_translation/src/Plugin/migrate/source/d6/I18nBlock.php
@@ -61,7 +61,7 @@
    */
   protected function initializeIterator() {
     $this->defaultTheme = $this->variableGet('theme_default', 'Garland');
-    $this->adminTheme = $this->variableGet('admin_theme', null);
+    $this->adminTheme = $this->variableGet('admin_theme', NULL);
     return parent::initializeIterator();
   }
 
@@ -72,12 +72,12 @@
     return [
       'bid' => $this->t('The block numeric identifier.'),
       'module' => $this->t('The module providing the block.'),
-      'delta' => $this->t('The block\'s delta.'),
+      'delta' => $this->t("The block's delta."),
       'theme' => $this->t('Which theme the block is placed in.'),
       'language' => $this->t('Language for this field.'),
       'property' => $this->t('Name of property being translated.'),
-      'translation' => $this->t('Translation of either the title or explanation.'
-    )];
+      'translation' => $this->t('Translation of either the title or explanation.'),
+    ];
   }
 
   /**
@@ -101,2 +101,3 @@
   }
+
 }
reverted:
--- b/core/modules/config_translation/tests/src/Unit/Plugin/migrate/source/d6/I18nBlockSourceTest.php
+++ /dev/null
@@ -1,161 +0,0 @@
-<?php
-
-namespace Drupal\Tests\config_translation\Unit\Plugin\migrate\source\d6;
-
-use Drupal\Tests\migrate\Unit\MigrateSqlSourceTestCase;
-
-/**
- * Tests i18n string block source plugin.
- *
- * @group config_translation
- */
-class I18nBlockSourceTest extends MigrateSqlSourceTestCase {
-
-  const PLUGIN_CLASS = 'Drupal\config_translation\Plugin\migrate\source\d6\I18nBlock';
-
-  protected $migrationConfiguration = [
-    'id' => 'id',
-    'source' => [
-      'plugin' => 'test',
-    ],
-  ];
-
-  protected $blocks = [
-    [
-      'bid' => 1,
-      'module' => 'block',
-      'delta' => '1',
-      'theme' => 'garland',
-      'status' => 1,
-      'weight' => 0,
-      'region' => 'left',
-      'custom' => 0,
-      'throttle' => 0,
-      'visibility' => 1,
-      'pages' => '',
-      'title' => 'Test Title 01',
-      'cache' => -1,
-    ],
-    [
-      'bid' => 2,
-      'module' => 'block',
-      'delta' => '2',
-      'theme' => 'garland',
-      'status' => 1,
-      'weight' => 5,
-      'region' => 'right',
-      'custom' => 0,
-      'throttle' => 0,
-      'visibility' => 0,
-      'pages' => '<front>',
-      'title' => 'Test Title 02',
-      'cache' => -1,
-    ],
-  ];
-
-  protected $i18n_strings = [
-    [
-      'lid' => 1,
-      'objectid' => 1,
-      'type' => 'block',
-      'property' => 'title',
-      'objectindex' => 0,
-      'format' => 0,
-    ],
-    [
-      'lid' => 2,
-      'objectid' => 1,
-      'type' => 'block',
-      'property' => 'body',
-      'objectindex' => 0,
-      'format' => 0,
-    ],
-    [
-      'lid' => 3,
-      'objectid' => 2,
-      'type' => 'block',
-      'property' => 'body',
-      'objectindex' => 0,
-      'format' => 2,
-    ]
-  ];
-
-  protected $locales_target = [
-    [
-      'lid' => 1,
-      'language' => 'fr',
-      'translation' => 'fr - title translation',
-      'plid' => 0,
-      'plural' => 0,
-      'u18n_status' => 0,
-    ],
-    [
-      'lid' => 2,
-      'language' => 'fr',
-      'translation' => 'fr - description translation',
-      'plid' => 0,
-      'plural' => 0,
-      'u18n_status' => 0,
-    ],
-    [
-      'lid' => 3,
-      'language' => 'zu',
-      'translation' => 'zu - description translation',
-      'plid' => 0,
-      'plural' => 0,
-      'u18n_status' => 0,
-    ],
-  ];
-
-  protected $expectedResults = [
-    [
-      'lid' => '1',
-      'type' => 'block',
-      'property' => 'title',
-      'objectid' => '1',
-      'lt_lid' => '1',
-      'language' => 'fr',
-      'translation' => 'fr - title translation',
-      'bid' =>  '1',
-      'module' => 'block',
-      'delta' => '1',
-    ],
-    [
-      'lid' => '2',
-      'type' => 'block',
-      'property' => 'body',
-      'objectid' => '1',
-      'lt_lid' => '2',
-      'language' => 'fr',
-      'translation' => 'fr - description translation',
-      'bid' =>  '1',
-      'module' => 'block',
-      'delta' => '1',
-    ],
-    [
-      'lid' => '3',
-      'type' => 'block',
-      'property' => 'body',
-      'objectid' => '2',
-      'lt_lid' => '3',
-      'language' => 'zu',
-      'translation' => 'zu - description translation',
-      'bid' =>  '2',
-      'module' => 'block',
-      'delta' => '2',
-    ],
-  ];
-
-  /**
-   * {@inheritdoc}
-   */
-  protected function setUp() {
-    $this->databaseContents['blocks'] = $this->blocks;
-    $this->databaseContents['i18n_strings'] = $this->i18n_strings;
-    $this->databaseContents['locales_target'] = $this->locales_target;
-
-    parent::setUp();
-  }
-
-}
-
diff -u b/core/modules/content_translation/src/Plugin/migrate/source/d6/I18nBox.php b/core/modules/content_translation/src/Plugin/migrate/source/d6/I18nBox.php
--- b/core/modules/content_translation/src/Plugin/migrate/source/d6/I18nBox.php
+++ b/core/modules/content_translation/src/Plugin/migrate/source/d6/I18nBox.php
@@ -34,6 +34,7 @@
    * Merge the block body and info translations into a single row.
    *
    * @return array
+   *   An array of ...
    */
   protected function values() {
     $values = [];
@@ -86,7 +87,7 @@
       'language' => $this->t('Language for this field.'),
       'body' => $this->t('The block/box content'),
       'info' => $this->t('Admin title of the block/box.'),
-      'format' => $this->t('Input format of the custom block/box content.')
+      'format' => $this->t('Input format of the custom block/box content.'),
     ];
   }
 
reverted:
--- b/core/modules/content_translation/tests/src/Unit/Plugin/migrate/source/d6/I18nBoxTest.php
+++ /dev/null
@@ -1,149 +0,0 @@
-<?php
-
-namespace Drupal\Tests\content_translation\Unit\Plugin\migrate\source\d6;
-
-use Drupal\Tests\migrate\Unit\MigrateSqlSourceTestCase;
-use Symfony\Component\Validator\Constraints\Null;
-
-/**
- * Tests i18n block title source plugin.
- *
- * @group content_translation
- */
-class I18nBoxTest extends MigrateSqlSourceTestCase {
-
-  const PLUGIN_CLASS = 'Drupal\content_translation\Plugin\migrate\source\d6\I18nBox';
-
-  protected $migrationConfiguration = [
-    'id' => 'id',
-    'source' => [
-      'plugin' => 'test',
-    ],
-  ];
-  /**
-   * Sample block instance query results from the source.
-   */
-  protected $boxes = [
-    [
-      'bid' => 1,
-      'body' => 'box 1 body',
-      'info' => 'box 1 info',
-      'format' => '2',
-    ],
-    [
-      'bid' => 2,
-      'body' => 'box 2 body',
-      'info' => 'box 2 info',
-      'format' => '2',
-    ],
-  ];
-
-  protected $i18n_strings = [
-    [
-      'lid' => 1,
-      'objectid' => 1,
-      'type' => 'block',
-      'property' => 'title',
-      'objectindex' => 0,
-      'format' => 0,
-    ],
-    [
-      'lid' => 2,
-      'objectid' => 1,
-      'type' => 'block',
-      'property' => 'body',
-      'objectindex' => 0,
-      'format' => 0,
-    ],
-    [
-      'lid' => 3,
-      'objectid' => 2,
-      'type' => 'block',
-      'property' => 'body',
-      'objectindex' => 0,
-      'format' => 2,
-    ]
-  ];
-
-  protected $locales_target = [
-    [
-      'lid' => 1,
-      'language' => 'fr',
-      'translation' => 'fr - info translation',
-      'plid' => 0,
-      'plural' => 0,
-      'i18n_status' => 0,
-    ],
-    [
-      'lid' => 2,
-      'language' => 'fr',
-      'translation' => 'fr - body translation',
-      'plid' => 0,
-      'plural' => 0,
-      'i18n_status' => 0,
-    ],
-    [
-      'lid' => 2,
-      'language' => 'zu',
-      'translation' => 'zu - body translation',
-      'plid' => 0,
-      'plural' => 0,
-      'i18n_status' => 0,
-    ],
-  ];
-
-  protected $expectedResults = [
-    [
-      'lid' => '2',
-      'type' => 'block',
-      'property' => 'body',
-      'objectid' => '1',
-      'lt_lid' => '2',
-      'language' => 'fr',
-      'translation' => 'fr - body translation',
-      'bid' =>  '1',
-      'body' => 'fr - body translation',
-      'info' => 'fr - info translation',
-      'format' => '2',
-    ],
-    [
-      'lid' => '2',
-      'type' => 'block',
-      'property' => 'body',
-      'objectid' => '1',
-      'lt_lid' => '2',
-      'language' => 'zu',
-      'translation' => 'zu - body translation',
-      'bid' =>  '1',
-      'body' => 'zu - body translation',
-      'info' => 'box 1 info',
-      'format' => '2',
-    ],
-    [
-      'lid' => '3',
-      'type' => 'block',
-      'property' => 'body',
-      'objectid' => '2',
-      'lt_lid' => Null,
-      'language' => Null,
-      'translation' => Null,
-      'bid' =>  '2',
-      'body' => Null,
-      'info' => 'box 2 info',
-      'format' => '2',
-    ],
-  ];
-
-  /**
-   * {@inheritdoc}
-   */
-  protected function setUp() {
-    $this->databaseContents['boxes'] = $this->boxes;
-    $this->databaseContents['i18n_strings'] = $this->i18n_strings;
-    $this->databaseContents['locales_target'] = $this->locales_target;
-
-    parent::setUp();
-  }
-
-}
-
diff -u b/core/modules/migrate_drupal_ui/src/Form/MigrateUpgradeForm.php b/core/modules/migrate_drupal_ui/src/Form/MigrateUpgradeForm.php
--- b/core/modules/migrate_drupal_ui/src/Form/MigrateUpgradeForm.php
+++ b/core/modules/migrate_drupal_ui/src/Form/MigrateUpgradeForm.php
@@ -66,6 +66,10 @@
       'source_module' => 'block',
       'destination_module' => 'block',
     ],
+    'd6_i18n_block' => [
+      'source_module' => 'translation',
+      'destination_module' => 'config_translation',
+    ],
     'd7_block' => [
       'source_module' => 'block',
       'destination_module' => 'block',
only in patch2:
unchanged:
--- /dev/null
+++ b/core/modules/config_translation/tests/src/Kernel/Plugin/migrate/source/d6/I18nBlockSourceTest.php
@@ -0,0 +1,157 @@
+<?php
+
+namespace Drupal\Tests\config_translation\Kernel\Plugin\migrate\source\d7;
+
+use Drupal\Tests\migrate\Kernel\MigrateSqlSourceTestBase;
+
+/**
+ * Tests i18n string block source plugin.
+ *
+ * @covers Drupal\config_translation\Plugin\migrate\source\d6\I18nBlock
+ *
+ * @group config_translation
+ */
+class I18nBlockSourceTest extends MigrateSqlSourceTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public static $modules = ['config_translation', 'migrate_drupal'];
+
+  /**
+   * {@inheritdoc}
+   */
+  public function providerSource() {
+    $tests = [];
+
+    // The source data.
+    $tests[0]['database']['blocks'] = [
+      [
+        'bid' => 1,
+        'module' => 'block',
+        'delta' => '1',
+        'theme' => 'garland',
+        'status' => 1,
+        'weight' => 0,
+        'region' => 'left',
+        'custom' => 0,
+        'throttle' => 0,
+        'visibility' => 1,
+        'pages' => '',
+        'title' => 'Test Title 01',
+        'cache' => -1,
+      ],
+      [
+        'bid' => 2,
+        'module' => 'block',
+        'delta' => '2',
+        'theme' => 'garland',
+        'status' => 1,
+        'weight' => 5,
+        'region' => 'right',
+        'custom' => 0,
+        'throttle' => 0,
+        'visibility' => 0,
+        'pages' => '<front>',
+        'title' => 'Test Title 02',
+        'cache' => -1,
+      ],
+    ];
+
+    $tests[0]['database']['i18n_strings'] = [
+      [
+        'lid' => 1,
+        'objectid' => 1,
+        'type' => 'block',
+        'property' => 'title',
+        'objectindex' => 0,
+        'format' => 0,
+      ],
+      [
+        'lid' => 2,
+        'objectid' => 1,
+        'type' => 'block',
+        'property' => 'body',
+        'objectindex' => 0,
+        'format' => 0,
+      ],
+      [
+        'lid' => 3,
+        'objectid' => 2,
+        'type' => 'block',
+        'property' => 'body',
+        'objectindex' => 0,
+        'format' => 2,
+      ],
+    ];
+
+    $tests[0]['database']['locales_target'] = [
+      [
+        'lid' => 1,
+        'language' => 'fr',
+        'translation' => 'fr - title translation',
+        'plid' => 0,
+        'plural' => 0,
+        'u18n_status' => 0,
+      ],
+      [
+        'lid' => 2,
+        'language' => 'fr',
+        'translation' => 'fr - description translation',
+        'plid' => 0,
+        'plural' => 0,
+        'u18n_status' => 0,
+      ],
+      [
+        'lid' => 3,
+        'language' => 'zu',
+        'translation' => 'zu - description translation',
+        'plid' => 0,
+        'plural' => 0,
+        'u18n_status' => 0,
+      ],
+    ];
+
+    $tests[0]['expectedResults'] = [
+      [
+        'lid' => '1',
+        'type' => 'block',
+        'property' => 'title',
+        'objectid' => '1',
+        'lt_lid' => '1',
+        'language' => 'fr',
+        'translation' => 'fr - title translation',
+        'bid' => '1',
+        'module' => 'block',
+        'delta' => '1',
+      ],
+      [
+        'lid' => '2',
+        'type' => 'block',
+        'property' => 'body',
+        'objectid' => '1',
+        'lt_lid' => '2',
+        'language' => 'fr',
+        'translation' => 'fr - description translation',
+        'bid' => '1',
+        'module' => 'block',
+        'delta' => '1',
+      ],
+      [
+        'lid' => '3',
+        'type' => 'block',
+        'property' => 'body',
+        'objectid' => '2',
+        'lt_lid' => '3',
+        'language' => 'zu',
+        'translation' => 'zu - description translation',
+        'bid' => '2',
+        'module' => 'block',
+        'delta' => '2',
+      ],
+    ];
+
+    return $tests;
+  }
+
+}
only in patch2:
unchanged:
--- /dev/null
+++ b/core/modules/content_translation/tests/src/Kernel/Plugin/migrate/source/d6/I18nBoxTest.php
@@ -0,0 +1,143 @@
+<?php
+
+namespace Drupal\Tests\content_translation\Kernel\Plugin\migrate\source\d7;
+
+use Drupal\Tests\migrate\Kernel\MigrateSqlSourceTestBase;
+
+/**
+ * Tests i18n block title source plugin.
+ *
+ * @covers Drupal\content_translation\Plugin\migrate\source\d6\I18nBox
+ *
+ * @group content_translation
+ */
+class I18nBoxTest extends MigrateSqlSourceTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public static $modules = ['content_translation', 'migrate_drupal'];
+
+  /**
+   * {@inheritdoc}
+   */
+  public function providerSource() {
+    $tests = [];
+
+    // The source data.
+    $tests[0]['database']['boxes'] = [
+      [
+        'bid' => 1,
+        'body' => 'box 1 body',
+        'info' => 'box 1 info',
+        'format' => '2',
+      ],
+      [
+        'bid' => 2,
+        'body' => 'box 2 body',
+        'info' => 'box 2 info',
+        'format' => '2',
+      ],
+    ];
+
+    $tests[0]['database']['i18n_strings'] = [
+      [
+        'lid' => 1,
+        'objectid' => 1,
+        'type' => 'block',
+        'property' => 'title',
+        'objectindex' => 0,
+        'format' => 0,
+      ],
+      [
+        'lid' => 2,
+        'objectid' => 1,
+        'type' => 'block',
+        'property' => 'body',
+        'objectindex' => 0,
+        'format' => 0,
+      ],
+      [
+        'lid' => 3,
+        'objectid' => 2,
+        'type' => 'block',
+        'property' => 'body',
+        'objectindex' => 0,
+        'format' => 2,
+      ],
+    ];
+
+    $tests[0]['database']['locales_target'] = [
+      [
+        'lid' => 1,
+        'language' => 'fr',
+        'translation' => 'fr - info translation',
+        'plid' => 0,
+        'plural' => 0,
+        'i18n_status' => 0,
+      ],
+      [
+        'lid' => 2,
+        'language' => 'fr',
+        'translation' => 'fr - body translation',
+        'plid' => 0,
+        'plural' => 0,
+        'i18n_status' => 0,
+      ],
+      [
+        'lid' => 2,
+        'language' => 'zu',
+        'translation' => 'zu - body translation',
+        'plid' => 0,
+        'plural' => 0,
+        'i18n_status' => 0,
+      ],
+    ];
+
+    // The expected results.
+    $tests[0]['expected_results'] = [
+      [
+        'lid' => '2',
+        'type' => 'block',
+        'property' => 'body',
+        'objectid' => '1',
+        'lt_lid' => '2',
+        'language' => 'fr',
+        'translation' => 'fr - body translation',
+        'bid' => '1',
+        'body' => 'fr - body translation',
+        'info' => 'fr - info translation',
+        'format' => '2',
+      ],
+      [
+        'lid' => '2',
+        'type' => 'block',
+        'property' => 'body',
+        'objectid' => '1',
+        'lt_lid' => '2',
+        'language' => 'zu',
+        'translation' => 'zu - body translation',
+        'bid' => '1',
+        'body' => 'zu - body translation',
+        'info' => 'box 1 info',
+        'format' => '2',
+      ],
+      [
+        'lid' => '3',
+        'type' => 'block',
+        'property' => 'body',
+        'objectid' => '2',
+        'lt_lid' => NULL,
+        'language' => NULL,
+        'translation' => NULL,
+        'bid' => '2',
+        'body' => NULL,
+        'info' => 'box 2 info',
+        'format' => '2',
+      ],
+    ];
+
+    return $tests;
+  }
+
+}