class TranslationManager

class TranslationManager implements TranslationInterface, TranslatorInterface {
    
    /**
     * An unsorted array of arrays of active translators.
     *
     * An associative array. The keys are integers that indicate priority. Values
     * are arrays of TranslatorInterface objects.
     *
     * @var \Drupal\Core\StringTranslation\Translator\TranslatorInterface[][]
     *
     * @see \Drupal\Core\StringTranslation\TranslationManager::addTranslator()
     * @see \Drupal\Core\StringTranslation\TranslationManager::sortTranslators()
     */
    protected $translators = [];
    
    /**
     * An array of translators, sorted by priority.
     *
     * If this is NULL a rebuild will be triggered.
     *
     * @var null|\Drupal\Core\StringTranslation\Translator\TranslatorInterface[]
     *
     * @see \Drupal\Core\StringTranslation\TranslationManager::addTranslator()
     * @see \Drupal\Core\StringTranslation\TranslationManager::sortTranslators()
     */
    protected $sortedTranslators = NULL;
    
    /**
     * The default langcode used in translations.
     *
     * @var string
     *   A language code.
     */
    protected $defaultLangcode;
    
    /**
     * Constructs a TranslationManager object.
     *
     * @param \Drupal\Core\Language\LanguageDefault $default_language
     *   The default language.
     */
    public function __construct(LanguageDefault $default_language) {
        $this->defaultLangcode = $default_language->get()
            ->getId();
    }
    
    /**
     * Appends a translation system to the translation chain.
     *
     * @param \Drupal\Core\StringTranslation\Translator\TranslatorInterface $translator
     *   The translation interface to be appended to the translation chain.
     * @param int $priority
     *   The priority of the logger being added.
     *
     * @return $this
     */
    public function addTranslator(TranslatorInterface $translator, $priority = 0) {
        $this->translators[$priority][] = $translator;
        // Reset sorted translators property to trigger rebuild.
        $this->sortedTranslators = NULL;
        return $this;
    }
    
    /**
     * Sorts translators according to priority.
     *
     * @return \Drupal\Core\StringTranslation\Translator\TranslatorInterface[]
     *   A sorted array of translator objects.
     */
    protected function sortTranslators() {
        krsort($this->translators);
        return array_merge(...$this->translators);
    }
    
    /**
     * {@inheritdoc}
     */
    public function getStringTranslation($langcode, $string, $context) {
        if ($this->sortedTranslators === NULL) {
            $this->sortedTranslators = $this->sortTranslators();
        }
        foreach ($this->sortedTranslators as $translator) {
            $translation = $translator->getStringTranslation($langcode, $string, $context);
            if ($translation !== FALSE) {
                return $translation;
            }
        }
        // No translator got a translation.
        return FALSE;
    }
    
    /**
     * {@inheritdoc}
     */
    public function translate($string, array $args = [], array $options = []) {
        return new TranslatableMarkup($string, $args, $options, $this);
    }
    
    /**
     * {@inheritdoc}
     */
    public function translateString(TranslatableMarkup $translated_string) {
        return $this->doTranslate($translated_string->getUntranslatedString(), $translated_string->getOptions());
    }
    
    /**
     * Translates a string to the current language or to a given language.
     *
     * @param string $string
     *   A string containing the English text to translate.
     * @param array $options
     *   An associative array of additional options, with the following elements:
     *   - 'langcode': The language code to translate to a language other than
     *      what is used to display the page.
     *   - 'context': The context the source string belongs to.
     *
     * @return string
     *   The translated string.
     */
    protected function doTranslate($string, array $options = []) {
        // If a NULL langcode has been provided, unset it.
        if (!isset($options['langcode']) && array_key_exists('langcode', $options)) {
            unset($options['langcode']);
        }
        // Merge in options defaults.
        $options = $options + [
            'langcode' => $this->defaultLangcode,
            'context' => '',
        ];
        $translation = $this->getStringTranslation($options['langcode'], $string, $options['context']);
        return $translation === FALSE ? $string : $translation;
    }
    
    /**
     * {@inheritdoc}
     */
    public function formatPlural($count, $singular, $plural, array $args = [], array $options = []) {
        return new PluralTranslatableMarkup($count, $singular, $plural, $args, $options, $this);
    }
    
    /**
     * Sets the default langcode.
     *
     * @param string $langcode
     *   A language code.
     */
    public function setDefaultLangcode($langcode) {
        $this->defaultLangcode = $langcode;
    }
    
    /**
     * {@inheritdoc}
     */
    public function reset() {
        if ($this->sortedTranslators === NULL) {
            $this->sortedTranslators = $this->sortTranslators();
        }
        foreach ($this->sortedTranslators as $translator) {
            $translator->reset();
        }
    }

}