As anyone who uses foreign language support in WordPress 1.5 may have noticed, switching to language to something other than english slows down WordPress. On my server, no request was finished in under 2 seconds.
So I had a look at the „gettext.php“ and optimized it a little bit (pushes request time down to 0.1 secs again), and Danilo Segan (the author and maintainer of php-gettext) made a new release with these changes:
1. Download the package
2. Replace gettext.php and streams.php (in wp-includes)
Additionally you can replace
$input = new FileReader($mofile)
in function load_textdomain (wp-l10n.php) with
$input = new CachedFileReader($mofile)
which also saves a few microseconds.