$re = '/(\[(?P<string1>.*?)\])\s*(?P<string2>[^\(]*)\s*(\((?P<string3>.*)\))?/';
$str = '[string1...] string2 in english/chinese (string3...)?
[string1...] string2 in english/chinese
';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php