I think there is a difference between ActionDeleteTiddlerWidget and tm-delete-tiddler. Only the latter generates a confirmation dialogue.
$:/core/ui/Buttons/delete uses tm-delete-tiddler. The confirmation message is in $:/language/ConfirmDeleteTiddler -- You received this message because you are subscribed to the Google Groups "TiddlyWiki" group. To unsubscribe from this group and stop receiving emails from it, send an email to tiddlywiki+unsubscr...@googlegroups.com. To post to this group, send email to tiddlywiki@googlegroups.com. Visit this group at https://groups.google.com/group/tiddlywiki. To view this discussion on the web visit https://groups.google.com/d/msgid/tiddlywiki/f5b85921-9b76-4925-b188-3e376e94f932%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
