these properties are usualy only available if PCRE is compiled with "--enable-unicode-properties"
if you want to match any word but want to provide a fallback, you can do something like that:
<?php
if(@preg_match_all('/\p{L}+/u', $str, $arr) {
// fallback goes here
// for example just '/\w+/u' for a less acurate match
}
?>