<?php
error_reporting(-1);
mb_internal_encoding('utf-8');
header("Content-Type: text/html; charset=utf-8");
 
$example = "Hello world. Я помню чудное мнгнoвернье, переdо мной явилась ты. Как мимолетное видeние, как гeний чистой краcoты. Ты где-то тyт. Тecт. А вот eще парочкa.";
 
function findCorruption($text) {
 
	$regexp = '/([а-яё]*)([a-z]+)([а-яё]*)/ui';
	$brokenWords = [];
	$count = preg_match_all($regexp, $text, $brokenWords, PREG_SET_ORDER);
 
	$result = [];
	foreach ($brokenWords as $word) {
		$result[] = preg_replace($regexp, '$1[$2]$3', $word[0]);
	}
	return $result;
}
 
$test = findCorruption($example);
 
foreach ($test as $mistake) {
	echo "Опечатка в слове: $mistake.\n";
}

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