Easy Digital Downloads - Change the button text of a free download. Default is "Free - Add to Cart"

gistfile1.php

<?php

/**
 * Easy Digital Downloads
 * Change the button text of a free download. Default is "Free - Add to Cart"
*/
function sumobi_edd_free_download_text_args( $args ) {
	// Enter the button text for a free download
	$free_download_text = 'Free download';

	$variable_pricing = edd_has_variable_prices( $args['download_id'] );

	if ( $args['price'] && $args['price'] !== 'no' && ! $variable_pricing ) {
		$price = edd_get_download_price( $args['download_id'] );

		if ( 0 == $price ) {
			$args['text'] = $free_download_text;
		}
	}

	return $args;
}
add_filter( 'edd_purchase_link_args', 'sumobi_edd_free_download_text_args' );