Index: app/helpers/issues_helper.rb
===================================================================
--- app/helpers/issues_helper.rb	(revision 15361)
+++ app/helpers/issues_helper.rb	(working copy)
@@ -165,7 +165,7 @@
       :parent_issue_id => issue
     }
     attrs[:tracker_id] = issue.tracker unless issue.tracker.disabled_core_fields.include?('parent_issue_id')
-    link_to(l(:button_add), new_project_issue_path(issue.project, :issue => attrs))
+    link_to(l(:button_new_subtask), new_project_issue_path(issue.project, :issue => attrs))
   end
 
   class IssueFieldsRows
Index: config/locales/en.yml
===================================================================
--- config/locales/en.yml	(revision 15361)
+++ config/locales/en.yml	(working copy)
@@ -1044,6 +1044,7 @@
   button_close: Close
   button_reopen: Reopen
   button_import: Import
+  button_new_subtask: New subtask
 
   status_active: active
   status_registered: registered