... non è completo ma ci và vicino...
... non uso il tag [ p h p ] altrimenti gli slash vanno via
... per copiarti il codice fai il quote del mio commento e copialo da lì...
<?php
$char_special = array(
"\"" => """,
"&" => "&",
"\'" => "'",
"<" => "<",
">" => ">",
"\u00A0" => "",
"\u00A1" => "¡",
"\u00A2" => "¢",
"\u00A3" => "£",
"\u00A4" => "¤",
"\u00A5" => "¥",
"\u00A6" => "¦",
"\u00A7" => "§",
"\u00A8" => "¨",
"\u00A9" => "©",
"\u00AA" => "ª",
"\u00AB" => "«",
"\u00AC" => "¬",
"\u00AD" => "",
"\u00AE" => "®",
"\u00B0" => "°",
"\u00B1" => "±",
"\u00B2" => "²",
"\u00B3" => "³",
"\u00B4" => "´",
"\u00B5" => "µ",
"\u00B6" => "¶",
"\u00B7" => "·",
"\u00B8" => "¸",
"\u00B9" => "¹",
"\u00BA" => "º",
"\u00BB" => "»",
"\u00BC" => "¼",
"\u00BD" => "½",
"\u00BE" => "¾",
"\u00BF" => "¿",
"\u00C0" => "À",
"\u00C1" => "Á",
"\u00C2" => "Â",
"\u00C3" => "Ã",
"\u00C4" => "Ä",
"\u00C5" => "Å",
"\u00C6" => "Æ",
"\u00C7" => "Ç",
"\u00C8" => "È",
"\u00C9" => "É",
"\u00CA" => "Ê",
"\u00CB" => "Ë",
"\u00CC" => "Ì",
"\u00CD" => "Í",
"\u00CE" => "Î",
"\u00CF" => "Ï",
"\u00D0" => "Ð",
"\u00D1" => "Ñ",
"\u00D2" => "Ò",
"\u00D3" => "Ó",
"\u00D4" => "Ô",
"\u00D5" => "Õ",
"\u00D6" => "Ö",
"\u00D7" => "×",
"\u00D8" => "Ø",
"\u00D9" => "Ù",
"\u00DA" => "Ú",
"\u00DB" => "Û",
"\u00DC" => "Ü",
"\u00DD" => "Ý",
"\u00DE" => "Þ",
"\u00DF" => "ß",
"\u00E0" => "à",
"\u00E1" => "á",
"\u00E2" => "â",
"\u00E3" => "ã",
"\u00E4" => "ä",
"\u00E5" => "å",
"\u00E6" => "æ",
"\u00E7" => "ç",
"\u00E8" => "è",
"\u00E9" => "é",
"\u00EA" => "ê",
"\u00EB" => "ë",
"\u00EC" => "ì",
"\u00ED" => "í",
"\u00EE" => "î",
"\u00EF" => "ï",
"\u00F0" => "ð",
"\u00F1" => "ñ",
"\u00F2" => "ò",
"\u00F3" => "ó",
"\u00F4" => "ô",
"\u00F5" => "õ",
"\u00F6" => "ö",
"\u00F7" => "÷",
"\u00F8" => "ø",
"\u00F9" => "ù",
"\u00FA" => "ú",
"\u00FB" => "û",
"\u00FC" => "ü",
"\u00FD" => "ý",
"\u00FE" => "þ",
"\u00FF" => "ÿ",
"\u0152" => "Œ",
"\u0153" => "œ",
"\u0160" => "Š",
"\u0161" => "š",
"\u0178" => "Ÿ",
"\u0192" => "ƒ",
"\u02C6" => "ˆ",
"\u02DC" => "˜",
"\u03A9" => "Ω",
"\u03C0" => "π",
"\u2013" => "–",
"\u2014" => "—",
"\u2018" => "‘",
"\u2019" => "’",
"\u201A" => "‚",
"\u201C" => "“",
"\u201D" => "”",
"\u2020" => "†",
"\u2021" => "‡",
"\u2022" => "•",
"\u2026" => "…",
"\u2030" => "‰",
"\u2039" => "‹",
"\u203A" => "›",
"\u2044" => "⁄",
"\u20AC" => "€",
"\u2122" => "™",
"\u2202" => "∂",
"\u220F" => "∏",
"\u2211" => "∑",
"\u221A" => "√",
"\u221E" => "∞",
"\u222B" => "∫",
"\u2248" => "≈",
"\u2260" => "≠",
"\u2264" => "≤",
"\u2265" => "≥",
"\u25CA" => "◊");
$string = "Grazie mille per l'aiuto, \u00ec \u003 \u00fc \u00e8";
echo str_ireplace(array_keys($char_special), $char_special, $string);
?>