This is a known deficiency in Mac OS X (darwin i.e.).

One solution is to set PERL_BADLANG to 0 in your environment, which simply tells Perl to shut up about these sort of locale problems.

Obviously this could lead to hard to debug problems.
A better way would be to set your LC_ALL environment var to "C", which is the default locale Perl would use anyway.

The best (IMHO) way to set this for your own account is to use the following file as your ~/.MacOSX/environment.plist (this sets the environment for every process loaded - without depending on your login shell setting):

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple Computer//DTD PLIST 1.0//EN" "http://
+www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
        <key>LC_ALL</key>
        <string>"C"</string>
</dict>
</plist>
[download]

Log out, log out and be set.

Update:
Don't log out twice ;-) Log in after you log out, of course....grin

janx