$re = '/\{\{Template[^\{]*(?:\{\{[^\}]*\}\}[^\{]*)*?[^\{]*\}\}/ms';
$str = 'lots of gibberish
before what I want{{Template
| x = 1
| y = {{Convert|1|2}}|z= {{Convert|3|4}}}}more gibberish
here too. {{Other|test}}
lots of gibberish
before what I want{{Template
| x = 1
| y = 2|z= 3}}more gibberish
here too. {{Other|test}}';
preg_match_all($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