How to use the translate.translate function in translate

/** The timer interface
  * @type {object} */
const timer = require('timer');

/** The system module
  * @type {object} */
const system = runtime.level >= fs.ROOT_LEVEL ? require('system') : null;

/** The web page's document
  * @type {Document} */
const document = system ? system.window.document : null;

/** The translation function
  * @type {function} */
const tr = translate.translate;

// If the application was loaded as a launcher...
if(runtime.arguments.launcher) {
  debug.log('Running dolphin launcher...');

  // Run the launcher's file in the global's context
  system.loadScript(runtime.path + '/launcher.js', () => {
    debug.error(tr('Failed to load the launcher file'));
  });
} else {
  /** The translation package path
    * @type {string} */
  // NOTE: We load the translation only here because the launcher will have
  //       to load it by itself (translations are not synchronous between
  //       main and child processes)
  let tr_path = fs.makeAbsolute('translations/' + translate.language + '.ntp');