How to change i18n/l10n of #reply-title? (Old title: Comment reply link not working)

It is because you need to enqueue comment-reply.js which is required for the jQuery effect.

Place the following in your header.php file within your head tag:

if ( is_singular() && get_option( 'thread_comments' ) )
    wp_enqueue_script( 'comment-reply' );