// Demo version
$js = '{
	"cities": [{
		"id": 1,
		"region": "Алтайский край"
	}, {
		"id": 2,
		"region": "Калининградская область"
	}, {
		"id": 3,
		"region": "Брянская область"
	}]
}';
// #1 ------------------------------------------
$ecnd = utf8_encode($js); // Put it through utf8_encode
$decnd = utf8_decode($ecnd);  // Getting data utf8_decode

    // #2 -------------------------------------------
    header('Content-type: application/json;charset=utf-8'); // Add HEADER
    echo json_encode($js); 
    // #3 Option adding json_encode as second argument
    // ,JSON_UNESCAPED_UNICODE|JSON_UNESCAPED_SLASHES