mp-custom-shipping-weight-rate.php

<?php
/*
Plugin Name: [MarketPress] - Custom Shipping Rates
Plugin URI: https://premium.wpmudev.org/
Description: Custom shipping weight rates. Requires to use the Weight rate option in MarketPress settings
Author: Panos Lyrakis @ WPMUDEV
Author URI: https://premium.wpmudev.org/
License: GPLv2 or later
*/

add_filter( 'mp_calculate_shipping_weight_rate', function( $price, $total, $cart, $address1, $address2, $city, $state, $zip, $country, $selected_option ){

	$weight_rates_per_country = array(

		//Germany
		'DE' => array(
			'2' => 2, // 2 Kgs == 2$
			'5' => 4, // 5 kgs == 4 $ etc
			'10' => 8
		),
		//United Kingdom
		'GB' => array(
			'2' => 4,
			'5' => 6,
			'10' => 9
		),
		//United Kingdom
		'FR' => array(
			'2' => 1.5,
			'5' => 3,
			'10' => 7
		),

	);

	$weight = $cart->shipping_weight();

	if( isset( $weight_rates_per_country[ $country ] ) && ! empty( $weight_rates_per_country[ $country ] ) ){

		foreach( $weight_rates_per_country[ $country ] as $kg => $shipping ){
			if( $weight <= $kg ){
				return $shipping;
			}
		}

	}
	
	return $price;

}, 20, 10 );