import-translation-when-module-install.php

<?php

/**
 * Implements hook_locale_translation_projects_alter().
 */
function MODULENAME_locale_translation_projects_alter(&$projects) {

  $path_module = drupal_get_path('module', 'MODULENAME');
  $path_translation = $path_module . '/translations/%language.po';

  $projects['MODULENAME'] = [
    'info' => [
      'interface translation server pattern' => $path_translation,
    ],
  ];
}