FYI - Quick Cache does not cache pages with there are any wordpress_* cookies. Since you use wordpress_polylang, Quick Cache will not cache the page.
May I suggest making the cookie name configurable in wp-config.php with a contant?
For now, I've had to modify the code.php file like this:
// set a cookie to remember the language. check headers have not been sent to avoid ugly error if (!headers_sent() && (!isset($_COOKIE['polylang']) || $_COOKIE['polylang'] != $this->curlang->slug)) setcookie('polylang', $this->curlang->slug, time() + 31536000 /* 1 year */, COOKIEPATH, COOKIE_DOMAIN); if (!headers_sent() && isset($_COOKIE['wordpress_polylang'])) setcookie('wordpress_polylang', '', time() - 3600, COOKIEPATH, COOKIE_DOMAIN); // unset the old cookie - jsmoriss 2013-01-18
I've modified the cookie name everywhere else as well, but removing the old cookie is also very important. ;-)