use Gettext\Scanner\TwigScanner;
use Gettext\Generator\PoGenerator;
use Gettext\Translations;

//Create a new scanner, adding a translation for each domain we want to get:
$twigScanner = new TwigScanner(
    Translations::create('domain1'),
    Translations::create('domain2'),
    Translations::create('domain3')
);

//Set a default domain, so any translations with no domain specified, will be added to that domain
$twigScanner->setDefaultDomain('domain1');

//Extract all comments starting with 'notes:'
$twigScanner->extractCommentsStartingWith('notes:');

//Scan files
foreach (glob('*.twig') as $file) {
    $twigScanner->scanFile($file);
}

//Save the translations in .po files
$generator = new PoGenerator();

foreach ($twigScanner->getTranslations() as $domain => $translations) {
    $generator->generateFile($translations, "locales/{$domain}.po");
}