diff -u b/core/modules/block/tests/src/Kernel/Migrate/d6/MigrateBlockTest.php b/core/modules/block/tests/src/Kernel/Migrate/d6/MigrateBlockTest.php
--- b/core/modules/block/tests/src/Kernel/Migrate/d6/MigrateBlockTest.php
+++ b/core/modules/block/tests/src/Kernel/Migrate/d6/MigrateBlockTest.php
@@ -102,7 +102,7 @@
     $this->assertEntity('user', $visibility, 'sidebar_first', 'bartik', 0, '', '0');
 
     $visibility = [];
-    $this->assertEntity('user_1', $visibility, 'sidebar_first', 'bartik', 0, 'zu - Test Title 02', 'visible');
+    $this->assertEntity('user_1', $visibility, 'sidebar_first', 'bartik', 0, '', '0');
 
     $visibility['user_role']['id'] = 'user_role';
     $roles['authenticated'] = 'authenticated';
@@ -116,9 +116,9 @@
     $visibility = [];
     $settings = [
       'id' => 'system_menu_block',
-      'label' => '',
+      'label' => 'zu - Test Title 02',
       'provider' => 'system',
-      'label_display' => '0',
+      'label_display' => 'visible',
       'level' => 1,
       'depth' => 0,
     ];
diff -u b/core/modules/content_translation/migration_templates/d6_custom_block_translation.yml b/core/modules/content_translation/migration_templates/d6_custom_block_translation.yml
--- b/core/modules/content_translation/migration_templates/d6_custom_block_translation.yml
+++ b/core/modules/content_translation/migration_templates/d6_custom_block_translation.yml
@@ -11,6 +11,16 @@
   langcode: language
   type: 'constants/type'
   info: info
+  title:
+    plugin: i18n_translation
+    source:
+      - title_untranslated
+      - title_translated
+  description:
+    plugin: i18n_translation
+    source:
+      - description_untranslated
+      - description_translated
   'body/format':
     plugin: migration
     migration: d6_filter_format
diff -u b/core/modules/content_translation/src/Plugin/migrate/source/d6/BoxTranslation.php b/core/modules/content_translation/src/Plugin/migrate/source/d6/BoxTranslation.php
--- b/core/modules/content_translation/src/Plugin/migrate/source/d6/BoxTranslation.php
+++ b/core/modules/content_translation/src/Plugin/migrate/source/d6/BoxTranslation.php
@@ -2,6 +2,8 @@
 
 namespace Drupal\content_translation\Plugin\migrate\source\d6;
 
+use Drupal\Component\Utility\Unicode;
+use Drupal\migrate\Row;
 use Drupal\migrate_drupal\Plugin\migrate\source\DrupalSqlBase;
 
 /**
@@ -13,69 +15,65 @@
  */
 class BoxTranslation extends DrupalSqlBase {
 
-  const INFO = "CASE WHEN property = 'title' THEN translation ELSE info END";
-  const BODY = "CASE WHEN property = 'body' THEN translation ELSE body END";
-
   /**
    * {@inheritdoc}
    */
-  public function count() {
-    return $this->initializeIterator()->count();
+  public function query() {
+    // Build a query based on 18n_strings 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.
+    $query = $this->select('boxes', 'b')
+      ->fields('b', ['bid', 'body', 'info', 'format']);
+    $query->orderBy('b.bid');
+
+    // Add in the property, which is either title or description.
+    $query->leftJoin('i18n_strings', 'i18n', 'b.bid = i18n.objectid');
+    $query->isNotNull('i18n.lid');
+    $query->addField('i18n', 'lid');
+    $query->addField('i18n', 'property');
+
+    // Add in the translation for the property.
+    $query->leftJoin('locales_target', 'lt', 'i18n.lid = lt.lid');
+    $query->addField('lt', 'language');
+    $query->addField('lt', 'translation');
+    return $query;
   }
 
   /**
    * {@inheritdoc}
    */
-  protected function initializeIterator() {
-    return new \ArrayIterator($this->values());
-  }
-
-  /**
-   * Merge the block body and info translations into a single row.
-   *
-   * @return array
-   *   An array of ...
-   */
-  protected function values() {
-    $values = [];
-    $result = $this->prepareQuery()->execute()->FetchAll();
-    $cnt = count($result);
-    for ($i = 0; $i < $cnt; $i++) {
-      if (isset($result[$i])) {
-        $j = $i + 1;
-        if (isset($result[$j])) {
-          // If the same bid and language, then this is the info.
-          if ($result[$i]['bid'] == $result[$j]['bid'] and
-            $result[$i]['language'] == $result[$j]['language']
-          ) {
-            $result[$i]['info'] = $result[$j]['info'];
-            unset($result[$j]);
-          }
-        }
-        $values[] = $result[$i];
-      }
+  public function prepareRow(Row $row) {
+    $language = $row->getSourceProperty('language');
+    $bid = $row->getSourceProperty('bid');
+    if (empty($this->idMap->lookupDestinationIds([
+      'bid' => $bid,
+      'language' => $language,
+    ]))
+    ) {
+      $row->setSourceProperty('migrate', TRUE);
     }
-    return $values;
-  }
+    // Set untranslated values as defaults.
+    $row->setSourceProperty('title_untranslated', $row->getSourceProperty('link_title'));
+    $row->setSourceProperty('options', unserialize($row->getSourceProperty('options')));
+    $row->setSourceProperty('description_untranslated', Unicode::truncate($row->getSourceProperty('options/attributes/title'), 255));
+
+    // Save the translation for this property.
+    $property = $row->getSourceProperty('property');
+    $row->setSourceProperty($property . '_translated', $row->getSourceProperty('translation'));
 
-  /**
-   * {@inheritdoc}
-   */
-  public function query() {
+    // Get the translation for the property not already in the row.
+    $property2 = ($property == 'title') ? 'description' : 'title';
     $query = $this->select('i18n_strings', 'i18n')
-      ->fields('i18n', ['lid', 'type', 'property', 'objectid'])
-      ->fields('lt', ['lid', 'language', 'translation'])
-      ->fields('b', ['bid', 'body', 'info', 'format'])
-      ->orderBy('bid')
-      ->orderBy('language')
-      ->orderBy('property')
-      ->condition('i18n.type', 'block');
-    $query->addExpression(self::INFO, 'info');
-    $query->addExpression(self::BODY, 'body');
-    $query->leftJoin('boxes', 'b', 'b.bid = i18n.objectid');
-    $query->leftJoin('locales_target', 'lt', 'lt.lid = i18n.lid');
-
-    return $query;
+      ->fields('i18n', ['lid']);
+    $query
+      ->condition('i18n.property', $property2)
+      ->condition('i18n.objectid', $bid);
+    $query->leftJoin('locales_target', 'lt', 'i18n.lid = lt.lid');
+    $query->condition('lt.language', $language);
+    $query->addField('lt', 'translation');
+    $results = $query->execute()->fetchAssoc();
+    $row->setSourceProperty($property2 . '_translated', $results['translation']);
   }
 
   /**
@@ -85,9 +83,8 @@
     return [
       'bid' => $this->t('The block numeric identifier.'),
       '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.'),
+      'title' => $this->t('Menu link title translation.'),
+      'description' => $this->t('Menu link description translation.'),
     ];
   }
 
@@ -96,6 +93,7 @@
    */
   public function getIds() {
     $ids['bid']['type'] = 'integer';
+    $ids['bid']['alias'] = 'b';
     $ids['language']['type'] = 'string';
     return $ids;
   }
diff -u b/core/modules/content_translation/tests/src/Kernel/Migrate/d6/MigrateBlockContentTranslationTest.php b/core/modules/content_translation/tests/src/Kernel/Migrate/d6/MigrateBlockContentTranslationTest.php
--- b/core/modules/content_translation/tests/src/Kernel/Migrate/d6/MigrateBlockContentTranslationTest.php
+++ b/core/modules/content_translation/tests/src/Kernel/Migrate/d6/MigrateBlockContentTranslationTest.php
@@ -15,11 +15,17 @@
    * {@inheritdoc}
    */
   public static $modules = [
+    'aggregator',
+    'book',
     'block',
+    'comment',
+    'forum',
     'views',
     'block_content',
     'content_translation',
     'language',
+    'statistics',
+    'taxonomy',
   ];
 
   /**
@@ -27,6 +33,7 @@
    */
   protected function setUp() {
     parent::setUp();
+ //   $this->installConfig(['aggregator']);
     $this->installConfig(['block']);
     $this->installConfig(['block_content']);
     $this->installEntitySchema('block_content');
@@ -46,7 +53,7 @@
   /**
    * Tests the migration of block title translation.
    */
-  public function testI18nBlock() {
+  public function testBlockContentTranslation() {
     $config = \Drupal::service('language_manager')->getLanguageConfigOverride('zu', 'block.block.user_1');
     $this->assertSame('zu - Test Title 02', $config->get('settings.label'));
   }
diff -u b/core/modules/content_translation/tests/src/Kernel/Migrate/d6/MigrateCustomBlockContentTranslationTest.php b/core/modules/content_translation/tests/src/Kernel/Migrate/d6/MigrateCustomBlockContentTranslationTest.php
--- b/core/modules/content_translation/tests/src/Kernel/Migrate/d6/MigrateCustomBlockContentTranslationTest.php
+++ b/core/modules/content_translation/tests/src/Kernel/Migrate/d6/MigrateCustomBlockContentTranslationTest.php
@@ -22,6 +22,7 @@
     'config_translation',
     'content_translation',
     'language',
+    'statistics',
   ];
 
   /**
@@ -46,8 +47,10 @@
   /**
    * Tests the Drupal 6 i18n custom block strings to Drupal 8 migration.
    */
-  public function testBlockMigration() {
+  public function testCustomBlockContentTranslation() {
     /** @var BlockContent $block */
+    $block = BlockContent::load(1);
+
     $block = BlockContent::load(1)->getTranslation('fr');
     $this->assertSame('fr - Static Block', $block->label());
     $this->assertTrue(REQUEST_TIME <= $block->getChangedTime() && $block->getChangedTime() <= time());
diff -u b/core/modules/migrate_drupal/tests/fixtures/drupal6.php b/core/modules/migrate_drupal/tests/fixtures/drupal6.php
--- b/core/modules/migrate_drupal/tests/fixtures/drupal6.php
+++ b/core/modules/migrate_drupal/tests/fixtures/drupal6.php
@@ -662,7 +662,7 @@
   'throttle' => '0',
   'visibility' => '0',
   'pages' => '',
-  'title' => 'zu - Test Title 02',
+  'title' => '',
   'cache' => '-1',
 ))
 ->values(array(
@@ -731,7 +731,7 @@
   'throttle' => '0',
   'visibility' => '0',
   'pages' => '',
-  'title' => '',
+  'title' => 'zu - Test Title 02',
   'cache' => '-1',
 ))
 ->values(array(
@@ -8086,23 +8086,6 @@
   'mysql_character_set' => 'utf8',
 ));
 
-$connection->insert('i18n_blocks')
-->fields(array(
-  'ibid',
-  'module',
-  'delta',
-  'type',
-  'language',
-))
-->values(array(
-  'ibid' => '1',
-  'module' => 'user',
-  'delta' => '1',
-  'type' => '0',
-  'language' => 'zu',
-))
-->execute();
-
 $connection->schema()->createTable('i18n_strings', array(
   'fields' => array(
     'lid' => array(
@@ -8431,6 +8414,23 @@
   'mysql_character_set' => 'utf8',
 ));
 
+$connection->insert('i18n_blocks')
+->fields(array(
+  'ibid',
+  'module',
+  'delta',
+  'type',
+  'language',
+))
+->values(array(
+  'ibid' => '1',
+  'module' => 'user',
+  'delta' => '1',
+  'type' => '0',
+  'language' => 'zu',
+))
+->execute();
+
 $connection->schema()->createTable('i18n_strings', array(
   'fields' => array(
     'lid' => array(
diff -u b/core/modules/migrate_drupal_ui/src/Form/MigrateUpgradeForm.php b/core/modules/migrate_drupal_ui/src/Form/MigrateUpgradeForm.php
--- b/core/modules/migrate_drupal_ui/src/Form/MigrateUpgradeForm.php
+++ b/core/modules/migrate_drupal_ui/src/Form/MigrateUpgradeForm.php
@@ -86,10 +86,6 @@
       'source_module' => 'block',
       'destination_module' => 'block_content',
     ],
-    'd6_custom_block_translation' => [
-      'source_module' => 'i18n',
-      'destination_module' => 'content_translation',
-    ],
     'd7_custom_block' => [
       'source_module' => 'block',
       'destination_module' => 'block_content',
@@ -98,6 +94,10 @@
       'source_module' => 'block',
       'destination_module' => 'block_content',
     ],
+    'd6_custom_block_translation' => [
+      'source_module' => 'i18n',
+      'destination_module' => 'content_translation',
+    ],
     'd7_custom_block' => [
       'source_module' => 'block',
       'destination_module' => 'block_content',
only in patch2:
unchanged:
--- /dev/null
+++ b/core/modules/content_translation/src/Plugin/migrate/process/d6/i18nTranslation.php
@@ -0,0 +1,31 @@
+<?php
+
+namespace Drupal\content_translation\Plugin\migrate\process\d6;
+
+use Drupal\migrate\MigrateExecutableInterface;
+use Drupal\migrate\ProcessPluginBase;
+use Drupal\migrate\Row;
+
+/**
+ * Processes an i18n translation.
+ *
+ * @MigrateProcessPlugin(
+ *   id = "i18n_translation"
+ * )
+ */
+class i18nTranslation extends ProcessPluginBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function transform($value, MigrateExecutableInterface $migrate_executable, Row $row, $destination_property) {
+    list($untranslated, $translated) = $value;
+    if ($translated) {
+      return $translated;
+    }
+    else {
+      return $untranslated;
+    }
+  }
+
+}