[Polvo]

I've just installed this mod for v4.1.6. I found it needed a few alterations to work with GBP as the default currency. So here's my revised version of the original installation instructions. Thanks to koaloa for a nice mod.

X-Cart Multiple Currency Mod – for version 4.1.6 Gold
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Download zip file and open with password given in first post in this thread.

Start by going to Admin > General Settings and remove the default alternate currency code '€'.

Copy:
skin1/customer/top_menu.tpl.
modules/Multiple_Currency/config.php

Copy these three files. If your default currency is not USD then edit them all first changing 'USD' to your default currency eg 'GBP'.:
skin1/customer/main/alter_currency_value.tpl
skin1/customer/main/show_currency_options.tpl
modules/Multiple_Currency/func.php with functions

Edit your copy of admin/configuration.php and add the lines of code from the included version (search for the text koaconsulting.com to see where changes have been made). Note: This file copies the currency rates from the Admin config table to the currencies table on opening or clicking save.

Modify the table xcart_config by adding entries including your default currency eg:
INSERT INTO `xcart_config` VALUES ('currency_rate_usd', 'Rate for the US Dollar', '0', 'Multiple_Currency', 0, 'numeric', '1.0', '');
INSERT INTO `xcart_config` VALUES ('currency_rate_euro','Rate for the EURO', '0', 'Multiple_Currency', 0, 'numeric', '1.0', '');
INSERT INTO `xcart_config` VALUES ('currency_rate_gbp', 'Rate for the British Pound', '0', 'Multiple_Currency', 0, 'numeric', '1.0', '');

Modify the table xcart_currencies by adding a field called 'rate', setting it as 'double' and making sure the default value is set to zero.

You need to run these SQL commands:
INSERT INTO `xcart_languages` VALUES ('US', 'lbl_currencies', 'Currencies', 'Labels');
INSERT INTO `xcart_languages` VALUES ('US', 'option_title_Multiple_Currency', 'Multiple Currencies Options', 'Labels');
INSERT INTO `xcart_modules` VALUES (xx, 'Multiple_Currency', 'Enables users to select different currencies to be displayed.', 'Y');
(Where xx is next id number available).

Go into the Admin > Modules area. 'Multiple_Currency' should be listed and ticked. Click 'Configure' to set your exchange rates, your default currency should be set to 1.