Drupal 8.0.0 beta 12. More info: https://www.drupal.org/node/2514176

core/lib/Drupal/Core/StringTranslation/StringTranslationTrait.php

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+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\StringTranslation\StringTranslationTrait.
+ */
+
+namespace Drupal\Core\StringTranslation;
+
+/**
+ * Wrapper methods for \Drupal\Core\StringTranslation\TranslationInterface.
+ *
+ * Using this trait will add t() and formatPlural() methods to the class. These
+ * must be used for every translatable string, similar to how procedural code
+ * must use the global functions t() and \Drupal::translation()->formatPlural().
+ * This allows string extractor tools to find translatable strings.
+ *
+ * If the class is capable of injecting services from the container, it should
+ * inject the 'string_translation' service and assign it to
+ * $this->stringTranslation.
+ *
+ * @see \Drupal\Core\StringTranslation\TranslationInterface
+ * @see container
+ *
+ * @ingroup i18n
+ */
+trait StringTranslationTrait {
+
+  /**
+   * The string translation service.
+   *
+   * @var \Drupal\Core\StringTranslation\TranslationInterface
+   */
+  protected $stringTranslation;
+
+  /**
+   * Translates a string to the current language or to a given language.
+   *
+   * See the t() documentation for details.
+   */
+  protected function t($string, array $args = array(), array $options = array()) {
+    return $this->getStringTranslation()->translate($string, $args, $options);
+  }
+
+  /**
+   * Formats a string containing a count of items.
+   *
+   * See the \Drupal\Core\StringTranslation\TranslationInterface::formatPlural()
+   * documentation for details.
+   */
+  protected function formatPlural($count, $singular, $plural, array $args = array(), array $options = array()) {
+    return $this->getStringTranslation()->formatPlural($count, $singular, $plural, $args, $options);
+  }
+
+  /**
+   * Formats a translated string containing a count of items.
+   *
+   * See the
+   * \Drupal\Core\StringTranslation\TranslationInterface::formatPluralTranslated()
+   * documentation for details.
+   */
+  protected function formatPluralTranslated($count, $translated, array $args = array(), array $options = array()) {
+    return $this->getStringTranslation()->formatPluralTranslated($count, $translated, $args, $options);
+  }
+
+  /**
+   * Returns the number of plurals supported by a given language.
+   *
+   * See the
+   * \Drupal\Core\StringTranslation\TranslationInterface::getNumberOfPlurals()
+   * documentation for details.
+   */
+  protected function getNumberOfPlurals($langcode = NULL) {
+    return $this->getStringTranslation()->getNumberOfPlurals($langcode);
+  }
+
+  /**
+   * Gets the string translation service.
+   *
+   * @return \Drupal\Core\StringTranslation\TranslationInterface
+   *   The string translation service.
+   */
+  protected function getStringTranslation() {
+    if (!$this->stringTranslation) {
+      $this->stringTranslation = \Drupal::service('string_translation');
+    }
+
+    return $this->stringTranslation;
+  }
+
+  /**
+   * Sets the string translation service to use.
+   *
+   * @param \Drupal\Core\StringTranslation\TranslationInterface $translation
+   *   The string translation service.
+   *
+   * @return $this
+   */
+  public function setStringTranslation(TranslationInterface $translation) {
+    $this->stringTranslation = $translation;
+
+    return $this;
+  }
+
+}

core/lib/Drupal/Core/StringTranslation/TranslationInterface.php

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+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\StringTranslation\TranslationInterface.
+ */
+
+namespace Drupal\Core\StringTranslation;
+
+/**
+ * Interface for the translation.manager translation service.
+ *
+ * @ingroup i18n
+ */
+interface TranslationInterface {
+
+  /**
+   * Translates a string to the current language or to a given language.
+   *
+   * @param string $string
+   *   A string containing the English string to translate.
+   * @param array $args
+   *   An associative array of replacements to make after translation. Based
+   *   on the first character of the key, the value is escaped and/or themed.
+   *   See \Drupal\Component\Utility\SafeMarkup::format() for details.
+   * @param array $options
+   *   An associative array of additional options, with the following elements:
+   *   - 'langcode': The language code to translate to a language other than
+   *      what is used to display the page.
+   *   - 'context': The context the source string belongs to.
+   *
+   * @return string
+   *   The translated string.
+   *
+   * @see \Drupal\Component\Utility\SafeMarkup::format()
+   */
+  public function translate($string, array $args = array(), array $options = array());
+
+  /**
+   * Formats a string containing a count of items.
+   *
+   * This function ensures that the string is pluralized correctly. Since t() is
+   * called by this function, make sure not to pass already-localized strings to
+   * it. See formatPluralTranslated() for that.
+   *
+   * For example:
+   * @code
+   *   $output = $string_translation->formatPlural($node->comment_count, '1 comment', '@count comments');
+   * @endcode
+   *
+   * Example with additional replacements:
+   * @code
+   *   $output = $string_translation->formatPlural($update_count,
+   *     'Changed the content type of 1 post from %old-type to %new-type.',
+   *     'Changed the content type of @count posts from %old-type to %new-type.',
+   *     array('%old-type' => $info->old_type, '%new-type' => $info->new_type));
+   * @endcode
+   *
+   * @param int $count
+   *   The item count to display.
+   * @param string $singular
+   *   The string for the singular case. Make sure it is clear this is singular,
+   *   to ease translation (e.g. use "1 new comment" instead of "1 new"). Do not
+   *   use @count in the singular string.
+   * @param string $plural
+   *   The string for the plural case. Make sure it is clear this is plural, to
+   *   ease translation. Use @count in place of the item count, as in
+   *   "@count new comments".
+   * @param array $args
+   *   An associative array of replacements to make after translation. Instances
+   *   of any key in this array are replaced with the corresponding value.
+   *   Based on the first character of the key, the value is escaped and/or
+   *   themed. See \Drupal\Component\Utility\SafeMarkup::format(). Note that you do
+   *   not need to include @count in this array; this replacement is done
+   *   automatically for the plural cases.
+   * @param array $options
+   *   An associative array of additional options. See t() for allowed keys.
+   *
+   * @return string
+   *   A translated string.
+   *
+   * @see self::translate()
+   * @see t()
+   * @see \Drupal\Component\Utility\SafeMarkup::format()
+   * @see self::formatPluralTranslated
+   */
+  public function formatPlural($count, $singular, $plural, array $args = array(), array $options = array());
+
+  /**
+   * Formats an already translated string containing a count of items.
+   *
+   * This function ensures that the string is pluralized correctly. As opposed
+   * to the formatPlural() method, this method is designed to be invoked with
+   * a string already translated (such as with configuration translation).
+   *
+   * @param int $count
+   *   The item count to display.
+   * @param string $translation
+   *   The string containing the translation of a singular/plural pair. It may
+   *   contain any number of possible variants (depending on the language
+   *   translated to) separated by the value of the LOCALE_PLURAL_DELIMITER
+   *   constant.
+   * @param array $args
+   *   Associative array of replacements to make in the translation. Instances
+   *   of any key in this array are replaced with the corresponding value.
+   *   Based on the first character of the key, the value is escaped and/or
+   *   themed. See \Drupal\Component\Utility\SafeMarkup::format(). Note that you do
+   *   not need to include @count in this array; this replacement is done
+   *   automatically for the plural cases.
+   * @param array $options
+   *   An associative array of additional options. The 'context' key is not
+   *   supported because the passed string is already translated. Use the
+   *   'langcode' key to ensure the proper plural logic is used.
+   *
+   * @return string
+   *   The correct substring for the given $count with $args replaced.
+   *
+   * @see self::formatPlural()
+   * @see \Drupal\Component\Utility\SafeMarkup::format()
+   */
+  public function formatPluralTranslated($count, $translation, array $args = array(), array $options = array());
+
+   /**
+    * Returns the number of plurals supported by a given language.
+    *
+    * @param null|string $langcode
+    *   (optional) The language code. If not provided, the current language
+    *   will be used.
+    *
+    * @return int
+    *   Number of plural variants supported by the given language.
+    */
+   public function getNumberOfPlurals($langcode = NULL);
+
+}

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

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+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\StringTranslation\TranslationManager.
+ */
+
+namespace Drupal\Core\StringTranslation;
+
+use Drupal\Component\Utility\SafeMarkup;
+use Drupal\Core\Language\LanguageManagerInterface;
+use Drupal\Core\State\StateInterface;
+use Drupal\Core\StringTranslation\Translator\TranslatorInterface;
+
+/**
+ * Defines a chained translation implementation combining multiple translators.
+ */
+class TranslationManager implements TranslationInterface, TranslatorInterface {
+
+  /**
+   * The language manager.
+   *
+   * @var \Drupal\Core\Language\LanguageManagerInterface
+   */
+  protected $languageManager;
+
+  /**
+   * An array of active translators keyed by priority.
+   *
+   * @var array
+   *   Array of \Drupal\Core\StringTranslation\Translator\TranslatorInterface objects
+   */
+  protected $translators = array();
+
+  /**
+   * Holds the array of translators sorted by priority.
+   *
+   * If this is NULL a rebuild will be triggered.
+   *
+   * @var array
+   *   An array of path processor objects.
+   *
+   * @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;
+
+  /**
+   * The state service.
+   *
+   * @var \Drupal\Core\State\StateInterface
+   */
+  protected $state;
+
+  /**
+   * Constructs a TranslationManager object.
+   *
+   * @param \Drupal\Core\Language\LanguageManagerInterface $language_manager
+   *   The language manager.
+   * @param \Drupal\Core\State\StateInterface $state
+   *   (optional) The state service.
+   */
+  public function __construct(LanguageManagerInterface $language_manager, StateInterface $state = NULL) {
+    $this->languageManager = $language_manager;
+    $this->defaultLangcode = $language_manager->getDefaultLanguage()->getId();
+    $this->state = $state;
+  }
+
+  /**
+   * Initializes the injected language manager with the translation manager.
+   *
+   * This should be called right after instantiating the translation manager to
+   * make it available to the language manager without introducing a circular
+   * dependency.
+   */
+  public function initLanguageManager() {
+    $this->languageManager->setTranslation($this);
+  }
+
+  /**
+   * 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 \Drupal\Core\StringTranslation\TranslationManager
+   *   The called object.
+   */
+  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 array
+   *   A sorted array of translators objects.
+   */
+  protected function sortTranslators() {
+    $sorted = array();
+    krsort($this->translators);
+
+    foreach ($this->translators as $translators) {
+      $sorted = array_merge($sorted, $translators);
+    }
+    return $sorted;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getStringTranslation($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(), array $options = array()) {
+    $string = $this->doTranslate($string, $options);
+    if (empty($args)) {
+      return SafeMarkup::set($string);
+    }
+    else {
+      return SafeMarkup::format($string, $args);
+    }
+  }
+
+  /**
+   * Translates a string to the current language or to a given language.
+   *
+   * @param string $string
+   *   A string containing the English string 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 $options = array()) {
+    // Merge in defaults.
+    if (empty($options['langcode'])) {
+      $options['langcode'] = $this->defaultLangcode;
+    }
+    if (empty($options['context'])) {
+      $options['context'] = '';
+    }
+    $translation = $this->getStringTranslation($options['langcode'], $string, $options['context']);
+    return $translation === FALSE ? $string : $translation;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function formatPlural($count, $singular, $plural, array $args = array(), array $options = array()) {
+    $translatable_string = implode(LOCALE_PLURAL_DELIMITER, array($singular, $plural));
+    $translated_strings = $this->doTranslate($translatable_string, $options);
+    return $this->formatPluralTranslated($count, $translated_strings, $args, $options);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function formatPluralTranslated($count, $translation, array $args = array(), array $options = array()) {
+    $args['@count'] = $count;
+    $translated_array = explode(LOCALE_PLURAL_DELIMITER, $translation);
+
+    if ($count == 1) {
+      return SafeMarkup::format($translated_array[0], $args);
+    }
+
+    // Get the plural index through the gettext formula.
+    // @todo implement static variable to minimize function_exists() usage.
+    $index = (function_exists('locale_get_plural')) ? locale_get_plural($count, isset($options['langcode']) ? $options['langcode'] : NULL) : -1;
+    if ($index == 0) {
+      // Singular form.
+      $return = $translated_array[0];
+    }
+    else {
+      if (isset($translated_array[$index])) {
+        // N-th plural form.
+        $return = $translated_array[$index];
+      }
+      else {
+        // If the index cannot be computed or there's no translation, use
+        // the second plural form as a fallback (which allows for most flexibility
+        // with the replaceable @count value).
+        $return = $translated_array[1];
+      }
+    }
+
+    return SafeMarkup::format($return, $args);
+  }
+
+  /**
+   * 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) {
+      $translator->reset();
+    }
+  }
+
+  /**
+   * @inheritdoc.
+   */
+  public function getNumberOfPlurals($langcode = NULL) {
+    // If the state service is not injected, we assume 2 plural variants are
+    // allowed. This may happen in the installer for simplicity. We also assume
+    // 2 plurals if there is no explicit information yet.
+    if (isset($this->state)) {
+      $langcode = $langcode ?: $this->languageManager->getCurrentLanguage()->getId();
+      $plural_formulas = $this->state->get('locale.translation.plurals') ?: array();
+      if (isset($plural_formulas[$langcode]['plurals'])) {
+        return $plural_formulas[$langcode]['plurals'];
+      }
+    }
+    return 2;
+  }
+
+}

core/lib/Drupal/Core/StringTranslation/TranslationWrapper.php

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+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\StringTranslation\TranslationWrapper.
+ */
+
+namespace Drupal\Core\StringTranslation;
+
+/**
+ * Provides a class to wrap a translatable string.
+ *
+ * This class can be used to delay translating strings until the translation
+ * system is ready. This is useful for using translation in very low level
+ * subsystems like entity definition and stream wrappers.
+ *
+ * @see \Drupal\Core\Annotation\Translation
+ */
+class TranslationWrapper {
+  use StringTranslationTrait;
+
+  /**
+   * The string to be translated.
+   *
+   * @var string
+   */
+  protected $string;
+
+  /**
+   * The translation arguments.
+   *
+   * @var array
+   */
+  protected $arguments;
+
+  /**
+   * The translation options.
+   *
+   * @var array
+   */
+  protected $options;
+
+  /**
+   * Constructs a new class instance.
+   *
+   * Parses values passed into this class through the t() function in Drupal and
+   * handles an optional context for the string.
+   *
+   * @param string $string
+   *   The string that is to be translated.
+   * @param array $arguments
+   *   (optional) An array with placeholder replacements, keyed by placeholder.
+   * @param array $options
+   *   (optional) An array of additional options.
+   */
+  public function __construct($string, array $arguments = array(), array $options = array()) {
+    $this->string = $string;
+    $this->arguments = $arguments;
+    $this->options = $options;
+  }
+
+  /**
+   * Gets the untranslated string value stored in this translation wrapper.
+   *
+   * @return string
+   *   The string stored in this wrapper.
+   */
+  public function getUntranslatedString() {
+    return $this->string;
+  }
+
+  /**
+   * Gets a specific option from this translation wrapper.
+   *
+   * @param $name
+   *   Option name.
+   *
+   * @return mixed
+   *   The value of this option or empty string of option is not set.
+   */
+  public function getOption($name) {
+    return isset($this->options[$name]) ? $this->options[$name] : '';
+  }
+
+  /**
+   * Implements the magic __toString() method.
+   */
+  public function __toString() {
+    return $this->render();
+  }
+
+  /**
+   * Renders the object as a string.
+   *
+   * @return string
+   *   The translated string.
+   */
+  public function render() {
+    return $this->t($this->string, $this->arguments, $this->options);
+  }
+
+  /**
+   * Magic __sleep() method to avoid serializing the string translator.
+   */
+  public function __sleep() {
+    return array('string', 'arguments', 'options');
+  }
+
+}

core/lib/Drupal/Core/StringTranslation/Translator/CustomStrings.php

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+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\StringTranslation\Translator\CustomStrings.
+ */
+
+namespace Drupal\Core\StringTranslation\Translator;
+
+use Drupal\Core\Site\Settings;
+
+/**
+ * String translator using overrides from variables.
+ *
+ * This is a high performance way to provide a handful of string replacements.
+ * See settings.php for examples.
+ */
+class CustomStrings extends StaticTranslation {
+
+  /**
+   * The settings read only object.
+   *
+   * @var \Drupal\Core\Site\Settings
+   */
+  protected $settings;
+
+  /**
+   * Constructs a CustomStrings object.
+   *
+   * @param \Drupal\Core\Site\Settings $settings
+   *   The settings read only object.
+   */
+  public function __construct(Settings $settings) {
+    parent::__construct();
+    $this->settings = $settings;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function getLanguage($langcode) {
+    return $this->settings->get('locale_custom_strings_' . $langcode, array());
+  }
+
+}

core/lib/Drupal/Core/StringTranslation/Translator/FileTranslation.php

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+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\StringTranslation\Translator\FileTranslation.
+ */
+
+namespace Drupal\Core\StringTranslation\Translator;
+
+use Drupal\Component\Gettext\PoStreamReader;
+use Drupal\Component\Gettext\PoMemoryWriter;
+
+/**
+ * File based string translation.
+ *
+ * Translates a string when some systems are not available.
+ *
+ * Used during the install process, when database, theme, and localization
+ * system is possibly not yet available.
+ */
+class FileTranslation extends StaticTranslation {
+
+  /**
+   * Directory to find translation files in the file system.
+   *
+   * @var string
+   */
+  protected $directory;
+
+  /**
+   * Constructs a StaticTranslation object.
+   *
+   * @param string $directory
+   *   The directory to retrieve file translations from.
+   */
+  public function __construct($directory) {
+    parent::__construct();
+    $this->directory = $directory;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function getLanguage($langcode) {
+    // If the given langcode was selected, there should be at least one .po
+    // file with its name in the pattern drupal-$version.$langcode.po.
+    // This might or might not be the entire filename. It is also possible
+    // that multiple files end with the same suffix, even if unlikely.
+    $files = $this->findTranslationFiles($langcode);
+
+    if (!empty($files)) {
+      return $this->filesToArray($langcode, $files);
+    }
+    else {
+      return array();
+    }
+  }
+
+  /**
+   * Finds installer translations either for a specific or all languages.
+   *
+   * Filenames must match the pattern:
+   *  - 'drupal-[version].[langcode].po (if langcode is provided)
+   *  - 'drupal-[version].*.po (if no langcode is provided)
+   *
+   * @param string $langcode
+   *   (optional) The language code corresponding to the language for which we
+   *   want to find translation files. If omitted, information on all available
+   *   files will be returned.
+   *
+   * @return array
+   *   An associative array of file information objects keyed by file URIs as
+   *   returned by file_scan_directory().
+   *
+   * @see file_scan_directory()
+   */
+  public function findTranslationFiles($langcode = NULL) {
+    $files = file_scan_directory($this->directory, $this->getTranslationFilesPattern($langcode), array('recurse' => FALSE));
+    return $files;
+  }
+
+  /**
+   * Provides translation file name pattern.
+   *
+   * @param string $langcode
+   *   (optional) The language code corresponding to the language for which we
+   *   want to find translation files.
+   *
+   * @return string
+   *  String file pattern.
+   */
+  protected function getTranslationFilesPattern($langcode = NULL) {
+    // The file name matches: drupal-[release version].[language code].po
+    // When provided the $langcode is use as language code. If not provided all
+    // language codes will match.
+    return '!drupal-[0-9a-z\.-]+\.' . (!empty($langcode) ? preg_quote($langcode, '!') : '[^\.]+') . '\.po$!';
+  }
+
+  /**
+   * Reads the given Gettext PO files into a data structure.
+   *
+   * @param string $langcode
+   *   Language code string.
+   * @param array $files
+   *   List of file objects with URI properties pointing to read.
+   *
+   * @return array
+   *   Structured array as produced by a PoMemoryWriter.
+   *
+   * @see \Drupal\Component\Gettext\PoMemoryWriter
+   */
+  public static function filesToArray($langcode, array $files) {
+    $writer = new PoMemoryWriter();
+    $writer->setLangcode($langcode);
+    foreach ($files as $file) {
+      $reader = new PoStreamReader();
+      $reader->setURI($file->uri);
+      $reader->setLangcode($langcode);
+      $reader->open();
+      $writer->writeItems($reader, -1);
+    }
+    return $writer->getData();
+  }
+}

core/lib/Drupal/Core/StringTranslation/Translator/StaticTranslation.php

@@ -0,0 +1,72 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\StringTranslation\Translator\StaticTranslation.
+ */
+
+namespace Drupal\Core\StringTranslation\Translator;
+
+/**
+ * String translator with a static cache for translations.
+ *
+ * This is a high performance way to provide a handful of string replacements.
+ */
+class StaticTranslation implements TranslatorInterface {
+
+  /**
+   * String translations
+   *
+   * @var array
+   *   Array of cached translations indexed by language and context.
+   */
+  protected $translations;
+
+  /**
+   * Constructs a translator from an array of translations.
+   *
+   * @param array $translations
+   *   Array of override strings indexed by language and context
+   */
+  public function __construct($translations = array()) {
+    $this->translations = $translations;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getStringTranslation($langcode, $string, $context) {
+    if (!isset($this->translations[$langcode])) {
+      $this->translations[$langcode] = $this->getLanguage($langcode);
+    }
+    if (isset($this->translations[$langcode][$context][$string])) {
+      return $this->translations[$langcode][$context][$string];
+    }
+    else {
+      return FALSE;
+    }
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function reset() {
+    $this->translations = array();
+  }
+
+  /**
+   * Add translations for new language.
+   *
+   * @param string $langcode
+   *   The langcode of the language.
+   */
+  protected function getLanguage($langcode) {
+    // This class is usually a base class but we do not declare as abstract
+    // because it can be used on its own, by passing a simple array on the
+    // constructor. This can be useful while testing, but it does not support
+    // loading specific languages. All available languages should be passed
+    // in the constructor array.
+    return array();
+  }
+
+}

core/lib/Drupal/Core/StringTranslation/Translator/TranslatorInterface.php

@@ -0,0 +1,38 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\StringTranslation\Translator\TranslatorInterface.
+ */
+
+namespace Drupal\Core\StringTranslation\Translator;
+
+/**
+ * Interface for objects capable of string translation.
+ */
+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();
+
+}