Issue #2922149 by Renrhaf, sbesselsen: Default search API language filter support

src/ElasticSearch/Parameters/Builder/SearchBuilder.php

@@ -218,6 +218,12 @@ class SearchBuilder {
       drupal_set_message($e->getMessage(), 'error');
     }
 
+    $languages = $this->query->getLanguages();
+    if ($languages !== NULL) {
+      $this->query->getConditionGroup()
+        ->addCondition('_language', $languages, 'IN');
+    }
+
     // Filters.
     try {
       $parsed_query_filters = $this->getQueryFilters(
@@ -372,6 +378,7 @@ class SearchBuilder {
    */
   protected function getQueryFilters(ConditionGroupInterface $condition_group, array $index_fields) {
     $filters = [];
+    $backend_fields = ['_language' => TRUE];
 
     if (!empty($condition_group)) {
       $conjunction = $condition_group->getConjunction();
@@ -389,7 +396,7 @@ class SearchBuilder {
           }
 
           $field_id = $condition->getField();
-          if (!isset($index_fields[$field_id])) {
+          if (!isset($index_fields[$field_id]) && !isset ($backend_fields[$field_id])) {
             // TODO: proper exception.
             throw new \Exception(
               t(

src/ElasticSearch/Parameters/Factory/IndexFactory.php

@@ -113,7 +113,9 @@ class IndexFactory {
     $params = IndexFactory::index($index, TRUE);
 
     foreach ($items as $id => $item) {
-      $data = [];
+      $data = [
+        '_language' => $item->getLanguage(),
+      ];
       /** @var \Drupal\search_api\Item\FieldInterface $field */
       foreach ($item as $name => $field) {
         $field_type = $field->getType();
@@ -195,6 +197,10 @@ class IndexFactory {
       }
     }
 
+    $properties['_language'] = [
+      'type' => 'keyword',
+    ];
+
     $params['body'][$params['type']]['properties'] = $properties;
 
     // Allow other modules to alter index mapping before we create it.