aeiou

<?php

$re = '/((?:ā|á|ǎ|à))|((?:ê|ē|é|ě|è))|((?:ī|í|ǐ|ì))|((?:ō|ó|ǒ|ò))|((?:ū|ú|ǔ|ù))|((?:ǖ|ǘ|ǚ|ǜ|ü))/';
$str = '汉(hàn)语(yǔ)平(píng)阴(yīn)女(nǚ)娥(é) => 汉(han)语(yu)平(ping)阴(yin)女(nü)娥(e)';

$result = preg_replace_callback($re, function($match){
    $map = array(
        0 => 'a',
        1 => 'e',
        2 => 'i',
        3 => 'o',
        4 => 'u',
        5 => 'ü',
        );
    for($i = 0; $i <=5; $i++) {
        if(!empty($match[$i])) {
            return $map[$i];
        }
    }
    
}, $str);

echo $str . "\n";
echo $result;