<?php
$text = 'The refugee said "dam!"';
$bad_words = array("fug","schnitt","dam");
array_walk($bad_words, function($value, $key) { // this prepares the regex, requires PHP 5.3+ I think.
return preg_quote('~\b' . $value . '\b~i'); // \b means word boundary, like space, line-break, and I think period, dash, and many others. Prevends "refudgee" from being matched when searching for "fudge"
});
$good_words = array("fudge","shoot","dang");
$good_text = preg_replace($bad_words,$good_words,$text);