Is there a way to programmatically add translations for strings?

Question

Is there a way to programmatically add translations for strings (user interface translation), for example in hook_update_N()?

With Drupal 7, I could use the following code.

/**
 * Helper to manually add a single translation string.
 *
 * After adding strings use locale_clear_cache() for clearing caches.
 */
function locale_add_translation($source, $langcode, $translation, $context = '', $textgroup = 'default') {
  require_once DRUPAL_ROOT . '/includes/locale.inc';
 
  $report = &drupal_static(__FUNCTION__, array('additions' => 0, 'updates' => 0, 'deletes' => 0, 'skips' => 0));
  _locale_import_one_string_db($report, $langcode, $context, $source, $translation, $textgroup, 'Manual import via helper ' . __FUNCTION__ .'().', LOCALE_IMPORT_OVERWRITE);
}
 
/**
 * Helper to clear the locale cache.
 */
function locale_clear_cache() {
  require_once DRUPAL_ROOT . '/includes/locale.inc';
  // Clear locale cache.
  _locale_invalidate_js();
  cache_clear_all('locale:', 'cache', TRUE);
}

Answer 1

Put the following helper function in your custom module.

use \Drupal\locale\SourceString;

function mymodule_add_translation($source_string, $translated_string, $langcode) {
  // Find the existing source string.
  $storage = \Drupal::service('locale.storage');
  $string = $storage->findString(array('source' => $source_string));
  if (is_null($string)) {
    $string = new SourceString();
    $string->setString($source_string);
    $string->setStorage($storage);
    $string->save();
  }
  // Create the translation. If it already exists, it will be replaced.
  $storage->createTranslation(array(
    'lid' => $string->lid,
    'language' => $langcode,
    'translation' => $translated_string,
  ))->save();
}

Answer 2

Here is a function to create plural translations.

use Drupal\Component\Gettext\PoItem;
use Drupal\locale\SourceString;

function mymodule_add_plural_translation(array $source_strings, array $translated_strings, string $langcode): void {
  /** @var \Drupal\locale\StringStorageInterface $storage */
  $storage = \Drupal::service('locale.storage');

  $source_string = implode(PoItem::DELIMITER, $source_strings);

  $string = $storage->findString(['source' => $source_string]);

  // If the string is not yet translated, create a new source string.
  if (is_null($string)) {
    $string = new SourceString();
    $string->setString($source_string);
    $string->setStorage($storage);
    $string->save();
  }

  // Create translation. If one already exists, it will be replaced.
  $translation = $storage->createTranslation([
    'lid' => $string->lid,
    'language' => $langcode,
  ]);
  $translation->setPlurals($translated_strings);
  $translation->save();
}

Use it like this:

$source_strings = [
  'Discounted product',  // Singular string first.
  'Discounted products', // Plural string second.
];
$translated_strings = [
  'Reduziertes Produkt', // Singular string first.
  'Reduzierte Produkte', // Plural string second.
];
$langcode = 'de';

mymodule_add_plural_translation($source_strings, $translated_strings, $langcode);

Answer 3

Another sample with string context, like from $this->t('Weight', [], ['context' => 'Physical weight']).

use Drupal\locale\SourceString;

/**
 * Fix "weight" translation.
 */
function MYMODULE_update_N(&$sandbox) {
  $source_string = 'Weight';
  $context = 'Physical weight';
  $langcode = 'de';
  $translated_string = 'Gewicht';

  // Find existing source string. If it doesn't exist, it will be created.
  $storage = \Drupal::service('locale.storage');
  $string = $storage->findString(['source' => $source_string, 'context' => $context]);
  if (is_null($string)) {
    $string = new SourceString();
    $string
      ->setString($source_string)
      ->setValues(['context' => $context])
      ->setStorage($storage)
      ->save();
  }

  // Create translation. If one already exists, it will be replaced.
  $translation = $storage->createTranslation([
    'lid' => $string->getId(),
    'language' => $langcode,
    'translation' => $translated_string,
    'context' => $context,
  ])->save();
}