<?php

$test = ['abcd', 'èe', '€', 'àòùìéëü', 'àòùìéëü', 'tiësto', 'Héllo', 'ⓚ', 'ĀāĂă','представления'];
foreach ($test as $e) {
    $normalized = preg_replace('/[^A-Z|^a-z|^0-9]/', '', iconv('UTF-8', 'ASCII//TRANSLIT//IGNORE', $e));
    echo $e . ' --> ' . $normalized . PHP_EOL;
}