Live Coding a Simple WooCommerce Checkout Currency Switcher

add_filter( 'woocommerce_checkout_fields' , function( $fields ) {
	$fields['billing']['billing_currency'] = array(
		'label' => 'Select currency',
		'type' => 'select',
		'options' => array( 'EUR' => 'Euro', 'USD' => 'Dollars' ),
		'class' => array( 'form-row-wide update_totals_on_change' ),
		'clear' => true,
		'priority' => 41,
		'required' => true,
	);
	return $fields;
});

add_action( 'woocommerce_checkout_update_order_review', function( $post_data ) {
	parse_str( $post_data, $output );
	if ( $output['billing_currency'] ) {
		WC()->session->set( 'billing_currency', sanitize_text_field( $output['billing_currency'] ) );
	}
});

add_filter( 'woocommerce_checkout_get_value', function( $value, $field_name ) {
	if ( $field_name == 'billing_currency' ) {
		$value = WC()->session->get( 'billing_currency' ) ? WC()->session->get( 'billing_currency' ) : $value;
	}
	return $value;
}, 9999, 2 );

add_filter( 'woocommerce_currency', function( $currency ) {
	if ( is_admin() ) return $currency;
	if ( WC()->session->get( 'billing_currency' ) ) {
		$currency = WC()->session->get( 'billing_currency' );
	}
	return $currency;
});

add_action( 'woocommerce_before_calculate_totals', function( $cart ) {
	
	if ( is_admin() && ! defined( 'DOING_AJAX' ) ) return; 
    if ( did_action( 'woocommerce_before_calculate_totals' ) >= 2 ) return;
	
	if ( WC()->session->get( 'billing_currency' ) && WC()->session->get( 'billing_currency' ) !== get_option( 'woocommerce_currency' ) ) {
	
		// we have dollars!
		// 1 EUR to 1.07 USD
		
		foreach ( $cart->get_cart() as $cart_item_key => $cart_item ) {
			
			$product = $cart_item['data'];
			$price = $product->get_price();
			$product->set_price( $price * 1.07 );
			
		}
		
	}

});

add_filter( 'woocommerce_package_rates', function( $rates, $package ) {

	if ( WC()->session->get( 'billing_currency' ) && WC()->session->get( 'billing_currency' ) !== get_option( 'woocommerce_currency' ) ) {
		
		foreach ( $rates as $rate_id => $rate ) {
			$rate->cost = $rate->cost * 1.07;
		}
		
	}

	return $rates;
}, 9999, 2 );

add_action( 'woocommerce_after_checkout_form',function() {
   wc_enqueue_js( "
	  if ( $('#billing_country') == 'US') {
         $('#billing_currency_field').show();
      } else {
         $('#billing_currency_field').hide();
      }
      $('#billing_country').on('change',function() {
         if ($(this).val() == 'US') {
            $('#billing_currency_field').show();
         } else {
            $('#billing_currency_field').hide();
         }
      });
   " );
});