its there an error in custom press plugin?

Hi there,

I was trying to fix some errors on my site ( running soooooo sloooooow). And notice an error when activating custom press plugging. The log says:
PHP Notice: Use of undefined constant WPLANG - assumed 'WPLANG' in /..content/plugins/custompress/core/core.php on line 57.

I tried to put this in instead :
// People use both "_" and "-" versions for locale IDs en_GB en-GB
//Translate it all to dashes because that's the way the standard translation files for datepicker are named.
$wplang = str_replace('_', '-', 'WPLANG');
$lang = ($wplang == '') ? '' : substr($wplang, 0, 2); // Non specific locale

Just dont know if it is an error or what?