function detectUTF8($string)
{
return preg_match('%(?:
[\\xC2-\\xDF][\\x80-\\xBF] # non-overlong 2-byte
|\\xE0[\\xA0-\\xBF][\\x80-\\xBF] # excluding overlongs
|[\\xE1-\\xEC\\xEE\\xEF][\\x80-\\xBF]{2} # straight 3-byte
|\\xED[\\x80-\\x9F][\\x80-\\xBF] # excluding surrogates
|\\xF0[\\x90-\\xBF][\\x80-\\xBF]{2} # planes 1-3
|[\\xF1-\\xF3][\\x80-\\xBF]{3} # planes 4-15
|\\xF4[\\x80-\\x8F][\\x80-\\xBF]{2} # plane 16
)+%xs', $string);
}

function is_utf8($str) {
    $c=0; $b=0;
    $bits=0;
    $len=strlen($str);
    for($i=0; $i<$len; $i++){
        $c=ord($str[$i]);
        if($c > 128){
            if(($c >= 254)) return false;
            elseif($c >= 252) $bits=6;
            elseif($c >= 248) $bits=5;
            elseif($c >= 240) $bits=4;
            elseif($c >= 224) $bits=3;
            elseif($c >= 192) $bits=2;
            else return false;
            if(($i+$bits) > $len) return false;
            while($bits > 1){
                $i++;
                $b=ord($str[$i]);
                if($b < 128 || $b > 191) return false;
                $bits--;
            }
        }
    }
    return true;
}