Anything to UTF-8. Support for arrays and object to string conversion as well.

to_utf8.php

<?php

/**
 * Converts anything to UTF-8.
 *
 * @param $string                  string|object|array
 * @param $stringify_objects       bool|true
 * @param $throw_exceptions        bool|true
 *
 * @throws InvalidArgumentException
 * @throws RuntimeException
 *
 * @return array|string
 */
function to_utf8($string, $stringify_objects = true, $throw_exceptions = true)
{
    if ($stringify_objects && is_object($string) && method_exists($string, '__toString')) {
        $string = (string)$string;
    }
    if (is_array($string)) {
        $out = array();
        foreach ($string as $i => $v) {
            $out[to_utf8($i, $stringify_objects, $throw_exceptions)] = to_utf8($v, $stringify_objects, $throw_exceptions);
        }
        return $out;
    } elseif (is_string($string)) {
        $detected = mb_detect_encoding($string,
            'UTF-8, ASCII, ISO-8859-1, ISO-8859-2, ISO-8859-3, ISO-8859-4, ISO-8859-5, ISO-8859-6, ISO-8859-7, ISO-8859-8, ISO-8859-9, ISO-8859-10, ISO-8859-13, ISO-8859-14, ISO-8859-15, ISO-8859-16, Windows-1251, Windows-1252, Windows-1254', true);

        if (!$detected) {
            $msg = 'Unable to detect encoding of ' . var_export($string, true);
            if ($throw_exceptions) {
                throw new RuntimeException($msg);
            } else {
                trigger_error($msg, E_USER_ERROR);
            }
        } elseif (!in_array($detected, array('UTF-8', 'ASCII'))) {
            $string = mb_convert_encoding($string, 'UTF-8', $detected);
        }
    } elseif (!is_scalar($string) && $string) {
        $msg = 'Can not convert to string, expecting object with __toString, array or string: ' . var_export($string, true);

        if ($throw_exceptions) {
            throw new RuntimeException($msg);
        } else {
            trigger_error($msg, E_USER_ERROR);
        }
    }
    return $string;
}