http://concrete5.killerwhalesoft.com/blog/make-laravel-slug-support-utf8-characters/
bu bağlantıdaki yazılanlara göre aşağıdaki makroyu kullanarak sorunu hallettim
Str::macro('slug_utf8', function($title, $separator = '-')
{
//$title = static::ascii($title); //comment it out to suport farsi
$title = str_replace(['ı','ğ','ü','ş','ö','ç','İ','Ğ','Ü','Ş','Ö','Ç'],['i','g','u','s','o','c','I','G','U','S','O','C'],$title);
// Convert all dashes/underscores into separator
$flip = $separator == '-' ? '_' : '-';
$title = preg_replace('!['.preg_quote($flip).']+!u', $separator, $title);
// Remove all characters that are not the separator, letters, numbers, or whitespace.
$title = preg_replace('![^'.preg_quote($separator).'\pL\pN\s]+!u', '', mb_strtolower($title));
// Replace all separator characters and whitespace by a single separator
$title = preg_replace('!['.preg_quote($separator).'\s]+!u', $separator, $title);
return trim($title, $separator);
});