wget -O project.tmx http://api.crowdin.net/api/project/{project-identifier}/download-tm?key={project-key}

<?php
ini_set('auto_detect_line_endings', 1); // allows file support for macintosh
ini_set('default_socket_timeout', 5); // socket timeout, just in case

file_put_contents("project.tmx", file_get_contents("http://api.crowdin.net/api/project/{project-identifier}/download-tm?key={project-key}"));