<?php

$a = array ('x'=>'xex');
var_dump($a); //output: array(1) { ["x"]=> string(3) "xex" }

echo PHP_EOL . "----" . PHP_EOL;

echo (json_encode($a)); //output: {"x":"xex"}

echo PHP_EOL . "----" . PHP_EOL;

$a = array ('x'=>'xéx');
var_dump($a); //output: array(1) { ["x"]=> string(3) "xéx" }

echo PHP_EOL . "----" . PHP_EOL;

echo (json_encode($a));