tools for utf-8 strings

str_tool.php

<?php

/**
 * split utf-8 string to array of chars
 * @param string $str
 * @return array
 */
function chars_of($str) {
    return preg_split('/(?<!^)(?!$)/u', $str);
}

/**
 * utf-8 analog for strtr function
 * @param string $str
 * @param string $from
 * @param string $to
 * @return string
 */
function mb_strtr($str, $from, $to) {
    return strtr(
        $str,
        array_combine(
            chars_of($from),
            chars_of($to)
        )
    );
}