Mohit Aghera
--- a/core/modules/jsonapi/src/Controller/EntityResource.php
+++ b/core/modules/jsonapi/src/Controller/EntityResource.php
      foreach ($sort->fields() as $field) {
        $path = $this->fieldResolver->resolveInternalEntityQueryPath($resource_type, $field[Sort::PATH_KEY]);
        $direction = isset($field[Sort::DIRECTION_KEY]) ? $field[Sort::DIRECTION_KEY] : 'ASC';
-        $langcode = isset($field[Sort::LANGUAGE_KEY]) ? $field[Sort::LANGUAGE_KEY] : NULL;
+        $langcode = isset($field[Sort::LANGUAGE_KEY]) ? $field[Sort::LANGUAGE_KEY] : $this->languageManager->getCurrentLanguage(LanguageInterface::TYPE_CONTENT)->getId();