This tools solve the problem when target string
is like "head\u4f60\u597d\u4e16\u754ctail"
composer require crlt/unicode-utf8
<?php
require_once "vendor/autoload.php";
$test = new Crlt\Tools\Unicode2Utf();
echo $test->Transform("head\u4f60\u597d\u4e16\u754ctail");
MIT