In addition to Sezer Yalcin's tip.

This function splits a multibyte string into an array of characters. Comparable to str_split().

<?php
function mb_str_split( $string ) {
    # Split at all position not after the start: ^
    # and not before the end: $
    return preg_split('/(?<!^)(?!$)/u', $string );
}

$string   = '火车票';
$charlist = mb_str_split( $string );

print_r( $charlist );
?>

# Prints:
Array
(
    [0] => 火
    [1] => 车
    [2] => 票
)