Import Translations in Drupal 8 programmatically.

call.php

  importTranslations([drupal_get_path('profile', 'myprofile')."/translations/es.po"]);

ImportTranslations.php

function importTranslations( array $poFiles) {

  \Drupal::moduleHandler()->loadInclude('locale', 'translation.inc');
  \Drupal::moduleHandler()->loadInclude('locale', 'bulk.inc');

  $opt_langcode = 'es';
  $opt_set_customized = TRUE;
  $opt_replace_customized = TRUE;
  $opt_replace_not_customized = TRUE;

  if (!$poFiles) {
    if ($dir = Settings::get('custom_translations_directory')) {
      $poFiles = glob(DRUPAL_ROOT . DIRECTORY_SEPARATOR . $dir . DIRECTORY_SEPARATOR . '*.po');
    }
    else {
      \Drupal::logger('update')
        ->info(t('Nothing to do, no file given and no custom translation directory set.'));
    }
  }

  $importer_options = array_merge(_locale_translation_default_update_options(), [
    'langcode' => $opt_langcode,
    'customized' => $opt_set_customized ? LOCALE_CUSTOMIZED : LOCALE_NOT_CUSTOMIZED,
    'overwrite_options' => [
      'customized' => (int) $opt_replace_customized,
      'not_customized' => (int) $opt_replace_not_customized,
    ],
  ]);

  // Import language files.
  $files = [];
  $langcodes_to_import = [];
  foreach ($poFiles as $file_path) {
    // Ensure we have the file intended for upload.
    if (file_exists($file_path)) {
      $file = locale_translate_file_create($file_path);

      // Extract project, version and language code from the file name
      // Supported:
      // - {project}-{version}.{langcode}.po, {prefix}.{langcode}.po
      // - {langcode}.po
      // Note: $options['langcode'] will override file langcode.
      $file = locale_translate_file_attach_properties($file, $importer_options);
      if ($file->langcode == LanguageInterface::LANGCODE_NOT_SPECIFIED) {
        if (!$opt_langcode) {
          \Drupal::logger('update')
            ->error(t('Can not autodetect language of file @file', ['@file' => $file_path]));
          return;
        }
        $file->langcode = $opt_langcode;
        if (empty($file->version) && !empty($file->project) && !empty($file->langcode)) {
          $sources = locale_translation_get_status();
          $source = $sources[$file->project][$file->langcode];
          if (isset($source->version)) {
            $file->version = $source->version;
          }
        }
      }
      $langcodes_to_import[$file->langcode] = $file->langcode;
      $files[] = $file;
    }
    else {
      \Drupal::logger('update')
        ->error(t('File to import at @filepath not found.', ['@filepath' => $file_path]));
    }
  }

  $batch = locale_translate_batch_build($files, $importer_options);
  batch_set($batch);

  // Create or update all configuration translations for this language.
  if ($batch = locale_config_batch_update_components($importer_options, $langcodes_to_import)) {
    batch_set($batch);
  }

  \Drupal::logger('update')->info(t('Import complete.'));
}