August 17, 2015
Add this to functions.php; update the placeholder “Your Text Here” with your new badge text:
add_filter( 'woocommerce_sale_flash', 'wc_custom_replace_sale_text' ); function wc_custom_replace_sale_text( $html ) { return str_replace( __( 'Sale!', 'woocommerce' ), __( 'Your Text Here', 'woocommerce' ), $html ); }
Sourced here.
The sourced post also mentions a plugin (Sale Flash Pro) that allows you to bring the discount percentage into this badge area.