Translating Strings in Sprout Invoices

functions.php

<?php

/**
 * Example filter will translate/change the string "Description".
 * "Description" can be changed to whatever string you'd like to translate/change
 * just make sure to change the function name so you don't have any conflicts.
 */

function l10n_description( $text ) {
	return 'Beschrijving';
}
add_filter( 'si_string_'.sanitize_title( 'Description' ), 'l10n_description' );