有一种更简单的方法可以做到这一点，使用iconv-从用户注解来看，这似乎是您想要做的：汉字音译

// PHP.net User notes
<?php
    $string = "ʿABBĀSĀBĀD";

    echo iconv('UTF-8', 'ISO-8859-1//TRANSLIT', $string);
    // output: [nothing, and you get a notice]

    echo iconv('UTF-8', 'ISO-8859-1//IGNORE', $string);
    // output: ABBSBD

    echo iconv('UTF-8', 'ISO-8859-1//TRANSLIT//IGNORE', $string);
    // output: ABBASABAD
    // Yay! That's what I wanted!
?>

对你的字符编码要非常认真，这样你就可以在整个过程中的所有阶段保持相同的编码--前端，表单提交，源文件编码。PHP和表单中的默认编码是ISO-8859-1，在PHP 5.4之前，它变成了UTF8（终于！）。
这里有两个函数，你可以尝试一下。第一个来自CakePHP的flector类，叫做slug：

public static function slug($string, $replacement = '_') {
    $quotedReplacement = preg_quote($replacement, '/');

    $merge = array(
        '/[^\s\p{Ll}\p{Lm}\p{Lo}\p{Lt}\p{Lu}\p{Nd}]/mu' => ' ',
        '/\\s+/' => $replacement,
        sprintf('/^[%s]+|[%s]+$/', $quotedReplacement, $quotedReplacement) => '',
    );

    $map = self::$_transliteration + $merge;
    return preg_replace(array_keys($map), array_values($map), $string);
}

它依赖于self::$_transliteration数组，这与您在问题中所做的类似-您可以使用see the source for inflector on github。
另一个是我个人使用的一个函数，它是comes from here。

function slugify($text,$strict = false) {
    $text = html_entity_decode($text, ENT_QUOTES, 'UTF-8');
    // replace non letter or digits by -
    $text = preg_replace('~[^\\pL\d.]+~u', '-', $text);

    // trim
    $text = trim($text, '-');
    setlocale(LC_CTYPE, 'en_GB.utf8');
    // transliterate
    if (function_exists('iconv')) {
        $text = iconv('utf-8', 'us-ascii//TRANSLIT', $text);
    }

    // lowercase
    $text = strtolower($text);
    // remove unwanted characters
    $text = preg_replace('~[^-\w.]+~', '', $text);
    if (empty($text)) {
        return 'empty_$';
    }
    if ($strict) {
        $text = str_replace(".", "_", $text);
    }
    return $text;
}

这些函数所做的是从任意文本输入中音译和创建“slugs”，这是一个非常非常有用的东西，在制作Web应用程序时，你的工具箱中有。

这里有一种方法，可以灵活地决定哪些应该被丢弃，哪些应该被替换，这就是我目前的做法。
$string = '某个带有垃圾的字符串';

$replace = [
    '<' => '', '>' => '', ''' => '', '&' => '',
    '"' => '', 'À' => 'A', 'Á' => 'A', 'Â' => 'A', 'Ã' => 'A', 'Ä' => 'Ae',
    'Ä' => 'A', 'Å' => 'A', 'Ā' => 'A', 'Ą' => 'A', 'Ă' => 'A', 'Æ' => 'Ae',
    'Ç' => 'C', 'Ć' => 'C', 'Č' => 'C', 'Ĉ' => 'C', 'Ċ' => 'C', 'Ď' => 'D', 'Đ' => 'D',
    'Ð' => 'D', 'È' => 'E', 'É' => 'E', 'Ê' => 'E', 'Ë' => 'E', 'Ē' => 'E',
    'Ę' => 'E', 'Ě' => 'E', 'Ĕ' => 'E', 'Ė' => 'E', 'Ĝ' => 'G', 'Ğ' => 'G',
    'Ġ' => 'G', 'Ģ' => 'G', 'Ĥ' => 'H', 'Ħ' => 'H', 'Ì' => 'I', 'Í' => 'I',
    'Î' => 'I', 'Ï' => 'I', 'Ī' => 'I', 'Ĩ' => 'I', 'Ĭ' => 'I', 'Į' => 'I',
    'İ' => 'I', 'IJ' => 'IJ', 'Ĵ' => 'J', 'Ķ' => 'K', 'Ł' => 'L', 'Ľ' => 'L',
    'Ĺ' => 'L', 'Ļ' => 'L', 'Ŀ' => 'L', 'Ñ' => 'N', 'Ń' => 'N', 'Ň' => 'N',
    'Ņ' => 'N', 'Ŋ' => 'N', 'Ò' => 'O', 'Ó' => 'O', 'Ô' => 'O', 'Õ' => 'O',
    'Ö' => 'Oe', 'Ö' => 'Oe', 'Ø' => 'O', 'Ō' => 'O', 'Ő' => 'O', 'Ŏ' => 'O',
    'Œ' => 'OE', 'Ŕ' => 'R', 'Ř' => 'R', 'Ŗ' => 'R', 'Ś' => 'S', 'Š' => 'S',
    'Ş' => 'S', 'Ŝ' => 'S', 'Ș' => 'S', 'Ť' => 'T', 'Ţ' => 'T', 'Ŧ' => 'T',
    'Ț' => 'T', 'Ù' => 'U', 'Ú' => 'U', 'Û' => 'U', 'Ü' => 'Ue', 'Ū' => 'U',
    'Ü' => 'Ue', 'Ů' => 'U', 'Ű' => 'U', 'Ŭ' => 'U', 'Ũ' => 'U', 'Ų' => 'U',
    'Ŵ' => 'W', 'Ý' => 'Y', 'Ŷ' => 'Y', 'Ÿ' => 'Y', 'Ź' => 'Z', 'Ž' => 'Z',
    'Ż' => 'Z', 'Þ' => 'T', 'à' => 'a', 'á' => 'a', 'â' => 'a', 'ã' => 'a',
    'ä' => 'ae', 'ä' => 'ae', 'å' => 'a', 'ā' => 'a', 'ą' => 'a', 'ă' => 'a',
    'æ' => 'ae', 'ç' => 'c', 'ć' => 'c', 'č' => 'c', 'ĉ' => 'c', 'ċ' => 'c',
    'ď' => 'd', 'đ' => 'd', 'ð' => 'd', 'è' => 'e', 'é' => 'e', 'ê' => 'e',
    'ë' => 'e', 'ē' => 'e', 'ę' => 'e', 'ě' => 'e', 'ĕ' => 'e', 'ė' => 'e',
    'ƒ' => 'f', 'ĝ' => 'g', 'ğ' => 'g', 'ġ' => 'g', 'ģ' => 'g', 'ĥ' => 'h',
    'ħ' => 'h', 'ì' => 'i', 'í' => 'i', 'î' => 'i', 'ï' => 'i', 'ī' => 'i',
    'ĩ' => 'i', 'ĭ' => 'i', 'į' => 'i', 'ı' => 'i', 'ij' => 'ij', 'ĵ' => 'j',
    'ķ' => 'k', 'ĸ' => 'k', 'ł' => 'l', 'ľ' => 'l', 'ĺ' => 'l', 'ļ' => 'l',
    'ŀ' => 'l', 'ñ' => 'n', 'ń' => 'n', 'ň' => 'n', 'ņ' => 'n', 'ʼn' => 'n',
    'ŋ' => 'n', 'ò' => 'o', 'ó' => 'o', 'ô' => 'o', 'õ' => 'o', 'ö' => 'oe',
    'ö' => 'oe', 'ø' => 'o', 'ō' => 'o', 'ő' => 'o', 'ŏ' => 'o', 'œ' => 'oe',
    'ŕ' => 'r', 'ř' => 'r', 'ŗ' => 'r', 'š' => 's', 'ù' => 'u', 'ú' => 'u',
    'û' => 'u', 'ü' => 'ue', 'ū' => 'u', 'ü' => 'ue', 'ů' => 'u', 'ű' => 'u',
    'ŭ' => 'u', 'ũ' => 'u', 'ų' => 'u', 'ŵ' => 'w', 'ý' => 'y', 'ÿ' => 'y',
    'ŷ' => 'y', 'ž' => 'z', 'ż' => 'z', 'ź' => 'z', 'þ' => 't', 'ß' => 'ss',
    'ſ' => 'ss', 'ый' => 'iy', 'А' => 'A', 'Б' => 'B', 'В' => 'V', 'Г' => 'G',
    'Д' => 'D', 'Е' => 'E', 'Ё' => 'YO', 'Ж' => 'ZH', 'З' => 'Z', 'И' => 'I',
    'Й' => 'Y', 'К' => 'K', 'Л' => 'L', 'М' => 'M', 'Н' => 'N', 'О' => 'O',
    'П' => 'P', 'Р' => 'R', 'С' => 'S', 'Т' => 'T', 'У' => 'U', 'Ф' => 'F',
    'Х' => 'H', 'Ц' => 'C', 'Ч' => 'CH', 'Ш' => 'SH', 'Щ' => 'SCH', 'Ъ' => '',
    'Ы' => 'Y', 'Ь' => '', 'Э' => 'E', 'Ю' => 'YU', 'Я' => 'YA', 'а' => 'a',
    'б' => 'b', 'в' => 'v', 'г' => 'g', 'д' => 'd', 'е' => 'e', 'ё' => 'yo',
    'ж' => 'zh', 'з' => 'z', 'и' => 'i', 'й' => 'y', 'к' => 'k', 'л' => 'l',
    'м' => 'm', 'н' => 'n', 'о' => 'o', 'п' => 'p', 'р' => 'r', 'с' => 's',
    'т' => 't', 'у' => 'u', 'ф' => 'f', 'х' => 'h', 'ц' => 'c', 'ч' => 'ch',
    'ш' => 'sh', 'щ' => 'sch', 'ъ' => '', 'ы' => 'y', 'ь' => '', 'э' => 'e',
    'ю' => 'yu', 'я' => 'ya'
];

echo str_replace(array_keys($replace), $replace, $string);

自PHP〉= 5.4.0起

$translatedString = transliterator_transliterate('Any-Latin; Latin-ASCII; [\u0080-\u7fff] remove', $string);

字符串$chain和数组中的字符采用了相同的字符编码，很有可能$first_name字符串采用了不同的编码，因此这些字符不匹配，你可以尝试使用多字节字符串函数。
尝试mb_convert_encoding。您可能还想尝试使用HTML_ENTITIES作为to_encoding参数，这样您就不必担心字符将如何转换-它将是非常可预测的。
假设您对这个脚本的输入是UTF-8格式，那么从这里开始可能不错...

$first_name = mb_convert_encoding($first_name, "HTML-ENTITIES", "UTF-8");

希望我能早点找到这个线程。我做的函数（花了我太长时间）如下：

function CheckLetters($field){
    $letters = [
        0 => "a à á â ä æ ã å ā",
        1 => "c ç ć č",
        2 => "e é è ê ë ę ė ē",
        3 => "i ī į í ì ï î",
        4 => "l ł",
        5 => "n ñ ń",
        6 => "o ō ø œ õ ó ò ö ô",
        7 => "s ß ś š",
        8 => "u ū ú ù ü û",
        9 => "w ŵ",
        10 => "y ŷ ÿ",
        11 => "z ź ž ż",
    ];
    foreach ($letters as &$values){
        $newValue = substr($values, 0, 1);
        $values = substr($values, 2, strlen($values));
        $values = explode(" ", $values);
        foreach ($values as &$oldValue){
            while (strpos($field,$oldValue) !== false){
                $field = preg_replace("/" . $oldValue . '/', $newValue, $field, 1);
            }
        }
    }
    return $field;
}

简单函数。将字符串'ÁbÇÉfg'转换为'abc_efg'

/**
 * @param $str
 * @return mixed
 */
function sanitizeString($str) {
    $str = preg_replace('/[áàãâä]/ui', 'a', $str);
    $str = preg_replace('/[éèêë]/ui', 'e', $str);
    $str = preg_replace('/[íìîï]/ui', 'i', $str);
    $str = preg_replace('/[óòõôö]/ui', 'o', $str);
    $str = preg_replace('/[úùûü]/ui', 'u', $str);
    $str = preg_replace('/[ç]/ui', 'c', $str);
    $str = preg_replace('/[^a-z0-9]/i', '_', $str);
    $str = preg_replace('/_+/', '_', $str);

    return $str;
}

代码点火方式：

$this->load->helper('text');

$string = convert_accented_characters($string);

此函数使用一个配套配置文件application/config/foreign_chars.php来定义用于音译的to和from数组。
https://www.codeigniter.com/user_guide/helpers/text_helper.html#ascii_to_entities

function correctedText($txt=''){
  $ss = str_split($txt);
    
  for($i=0; $i<count($ss); $i++){
    $asciiNumber = ord($ss[$i]);// get the ascii dec of a single character
    
    // asciiNumber will be from the DEC column showing at https://www.ascii-code.com
    
    // capital letters only checked 
    if($asciiNumber >= 192 && $asciiNumber <= 197)$ss[$i] = 'A';
    elseif($asciiNumber == 198)$ss[$i] = 'AE';
    elseif($asciiNumber == 199)$ss[$i] = 'C';
    elseif($asciiNumber >= 200 && $asciiNumber <= 203)$ss[$i] = 'E';
    elseif($asciiNumber >= 204 && $asciiNumber <= 207)$ss[$i] = 'I';
    elseif($asciiNumber == 209)$ss[$i] = 'N';
    elseif($asciiNumber >= 210 && $asciiNumber <= 214)$ss[$i] = 'O';
    elseif($asciiNumber == 216)$ss[$i] = 'O';
    elseif($asciiNumber >= 217 && $asciiNumber <= 220)$ss[$i] = 'U';
    elseif($asciiNumber == 221)$ss[$i] = 'Y';
  }
    
  $txt = implode('', $ss);
    
  return $txt;
}