Update to Drupal 8.0.5. For more information, see https://www.drupal.org/node/2679347

core/modules/path/migration_templates/d6_url_alias.yml

@@ -17,6 +17,8 @@ process:
     source:
       - constants/slash
       - dst
-  langcode: language
+  langcode:
+    plugin: d6_url_alias_language
+    source: language
 destination:
   plugin: url_alias

core/modules/path/src/Plugin/migrate/process/d6/UrlAliasLanguage.php

@@ -0,0 +1,32 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\path\Plugin\migrate\process\d6\UrlAliasLanguage.
+ */
+
+namespace Drupal\path\Plugin\migrate\process\d6;
+
+use Drupal\migrate\MigrateExecutableInterface;
+use Drupal\migrate\ProcessPluginBase;
+use Drupal\migrate\Row;
+use Drupal\Core\Language\LanguageInterface;
+
+/**
+ * Url alias language code process.
+ *
+ * @MigrateProcessPlugin(
+ *   id = "d6_url_alias_language"
+ * )
+ */
+class UrlAliasLanguage extends ProcessPluginBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function transform($value, MigrateExecutableInterface $migrate_executable, Row $row, $destination_property) {
+    $langcode = ($value === '') ? LanguageInterface::LANGCODE_NOT_SPECIFIED : $value;
+    return $langcode;
+  }
+
+}

core/modules/path/src/Tests/Migrate/d6/MigrateUrlAliasTest.php

@@ -33,27 +33,44 @@ class MigrateUrlAliasTest extends MigrateDrupal6TestBase {
     $this->executeMigration('d6_url_alias');
   }
 
+  /**
+   * Assert a path.
+   *
+   * @param string pid
+   *   The path id.
+   * @param array $conditions
+   *   The path conditions.
+   * @param array $path
+   *   The path.
+   */
+  private function assertPath($pid, $conditions, $path) {
+    $this->assertTrue($path, "Path alias for " . $conditions['source'] . " successfully loaded.");
+    $this->assertIdentical($conditions['alias'], $path['alias']);
+    $this->assertIdentical($conditions['langcode'], $path['langcode']);
+    $this->assertIdentical($conditions['source'], $path['source']);
+  }
+
   /**
    * Test the url alias migration.
    */
   public function testUrlAlias() {
     $id_map = Migration::load('d6_url_alias')->getIdMap();
-    // Test that the field exists.
     $conditions = array(
       'source' => '/node/1',
       'alias' => '/alias-one',
-      'langcode' => 'en',
+      'langcode' => 'af',
     );
     $path = \Drupal::service('path.alias_storage')->load($conditions);
-    $this->assertNotNull($path, "Path alias for node/1 successfully loaded.");
+    $this->assertPath('1', $conditions, $path);
     $this->assertIdentical($id_map->lookupDestinationID(array($path['pid'])), array('1'), "Test IdMap");
+
     $conditions = array(
       'source' => '/node/2',
       'alias' => '/alias-two',
       'langcode' => 'en',
     );
     $path = \Drupal::service('path.alias_storage')->load($conditions);
-    $this->assertNotNull($path, "Path alias for node/2 successfully loaded.");
+    $this->assertPath('2', $conditions, $path);
 
     // Test that we can re-import using the UrlAlias destination.
     Database::getConnection('default', 'migrate')
@@ -72,7 +89,16 @@ class MigrateUrlAliasTest extends MigrateDrupal6TestBase {
     $this->executeMigration($migration);
 
     $path = \Drupal::service('path.alias_storage')->load(array('pid' => $path['pid']));
-    $this->assertIdentical('/new-url-alias', $path['alias']);
+    $conditions['alias'] = '/new-url-alias';
+    $this->assertPath('2', $conditions, $path);
+
+    $conditions = array(
+      'source' => '/node/3',
+      'alias' => '/alias-three',
+      'langcode' => 'und',
+    );
+    $path = \Drupal::service('path.alias_storage')->load($conditions);
+    $this->assertPath('3', $conditions, $path);
   }
 
 }