interface TranslatorInterface

1. 8.x drupal/core/lib/Drupal/Core/StringTranslation/Translator/TranslatorInterface.php \Drupal\Core\StringTranslation\Translator\TranslatorInterface
2. 8.x drupal/core/vendor/symfony/translation/Symfony/Component/Translation/TranslatorInterface.php \Symfony\Component\Translation\TranslatorInterface

LanguageRequestSubscriber.php in drupal/core/lib/Drupal/Core/EventSubscriber/LanguageRequestSubscriber.php

Contains \Drupal\Core\EventSubscriber\LanguageRequestSubscriber.

LocaleTranslation.php in drupal/core/modules/locale/lib/Drupal/locale/LocaleTranslation.php

Contains \Drupal\Core\Language\LocaleTranslation.

TranslationManager.php in drupal/core/lib/Drupal/Core/StringTranslation/TranslationManager.php

Contains \Drupal\Core\StringTranslation\TranslationManager.

interface TranslatorInterface {

  /**
   * Retrieves English string to given language.
   *
   * @param string $langcode
   *   Language code to translate to.
   * @param string $string
   *   The source string.
   * @param string $context
   *   The string context.
   *
   * @return string|FALSE
   *   Translated string if there is a translation, FALSE if not.
   */
  public function getStringTranslation($langcode, $string, $context);

  /**
   * Resets translation cache.
   *
   * Since most translation systems implement some form of caching, this
   * provides a way to delete that cache.
   */
  public function reset();

}