The final solution of plural and singular terms name is below.
Code
<?php $term_ids = wp_get_post_terms( $product->get_id(), 'variety', array('fields' => 'ids') );
echo get_the_term_list( $product->get_id(), 'variety', '<span class="posted_in">' . _n( 'Ποικιλία:', 'Ποικιλίες:', count( $term_ids ), 'text-domain' ) . ' ', ', ', '</span>' ); ?>
In my project is working correct 🙂
Hope to help anyone to fix this issue !