Thanks a lot, it worked. I did the following:
Title: addonname_threads_list_deleted
Phrase text: This thread, started by {create_user}, has been deleted by {deleted_user}, {deleted_date}
Usage: {xen:phrase addonname_threads_list_deleted, 'create_user=User1', 'deleted_user=User2', 'deleted_date=Today'}
Is it possible to replace User1 with <xen:username user="{$threads.create}" rich="true" />?