$re = '/(?<!\S)[^а-яА-Я\s]+(?!\S)/m';
$str = ' des поместья, de la famille Buonaparte. Non, je vous préviens que si vous поместья поместья test поместья
';
$subst = "";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php