/**
 * Implements hook_locale_translation_projects_alter().
 */
function {{ machine_name }}_locale_translation_projects_alter(&$projects) {
  // The translations are located at a custom translation sever.
  $projects['existing_project'] = [
    'info' => [
      'interface translation server pattern' => 'http://example.com/files/translations/%core/%project/%project-%version.%language.po',
    ],
  ];
}