% cd /System/Library/CoreServices/Dock.app/Contents/Resources/English.lproj(don't type the % signs; those are the command-line prompt symbols)
% sudo vi InfoPlist.strings
This one-line file contains the name for the trash can. Change the name, save the file (in vi, use 'w!' to override the read-only warning), quit the dock (see the comments for a clean way to do this!), it will restart, and you'll have a new name on your trash.

