Stuck with sidebar registering

get_sidebar('dfth') looks for a sidebar-dfth.php file in your template directory. If not found, it loads the default sidebar. To call the sidebar you registered in a template, use e.g.

<?php if ( is_active_sidebar( 'dfth' ) ) : ?>
<div class="first dfth-widgets">
    <?php dynamic_sidebar( 'dfth' ); ?>
</div><!-- .first -->
<?php endif; ?>