<?php

$str = 'mes "teste de mensagem";
input "blablabla";
switch("este é um":"placeholder");
end script;';


$regex = '/[.*\n]?"(.+?)"[.*\n]?(?1)*?/';

//preg_match($regex, $str, $matches);
preg_match_all($regex, $str, $matches);

print_r($matches);