class.string.tr.php

class STR
{
    private static $tr_lo = array("ı", "ğ", "ü", "ş", "i", "ö", "ç");
    private static $tr_up = array("I", "Ğ", "Ü", "Ş", "İ", "Ö", "Ç");

    public static function strtolower($str, $encoding = "UTF-8")
    {
        return mb_convert_case(str_replace(self::$tr_up, self::$tr_lo, $str), MB_CASE_LOWER, $encoding);
    }

    public static function strtoupper($str, $encoding = "UTF-8")
    {
        return mb_convert_case(str_replace(self::$tr_lo, self::$tr_up, $str), MB_CASE_UPPER, $encoding);
    }

    public static function ucwords($str, $encoding = "UTF-8")
    {
        $return = array();
        $words = str_word_count($str, 1, implode(self::$tr_lo) . implode(self::$tr_up));
        foreach ($words as $word) {
            $return[] = self::ucfirst(self::strtolower($word), true, $encoding);
        }
        return implode($return, " ");
    }

    public static function ucfirst($str, $lower_str_end = false, $encoding = "UTF-8")
    {
        $first_letter = self::strtoupper(mb_substr($str, 0, 1, $encoding), $encoding);
        if ($lower_str_end) {
            $str_end = self::strtolower(mb_substr($str, 1, mb_strlen($str, $encoding), $encoding), $encoding);
        } else {
            $str_end = mb_substr($str, 1, mb_strlen($str, $encoding), $encoding);
        }
        $str = $first_letter . $str_end;
        return $str;
    }
}

sonuc.txt

IĞÜŞİÖÇ IĞÜŞİÖÇ DENEME
ığüşiöç ığüşiöç deneme
Iğüşiöç Iğüşiöç Deneme
IĞÜŞİÖÇ ığüşiöç deneme
Iğüşiöç ığüşiöç deneme

test.php

$metin = "IĞÜŞİÖÇ ığüşiöç deneme";
echo STR::strtoupper($metin);
echo "\n";
echo STR::strtolower($metin);
echo "\n";
echo STR::ucwords($metin);
echo "\n";
echo STR::ucfirst($metin);
echo "\n";
echo STR::ucfirst($metin,true);