Example:

$url = "http://domain.ext/filename.txt";
$result = system_retrieve_file($url, $destination = NULL, $managed = FALSE, $replace = FILE_EXISTS_REPLACE);

Programmatically create and translate nodes.

Programmatically create and translate menu links.

Example:

// Programmatically create files.
use Drupal\file\Entity\File;
$file = File::create([
  'uid' => 1,
  'filename' => 'test.txt',
  'uri' => 'public://page/test.txt',
  'status' => 1,
]);
$file->save();

Exemples:

$translation = $entity->getTranslation('de');