OpenCart is an ecommerce platform or in other words, software that allows you to build an online shop. Another open source project, so it’s available for free. If you’d like to see an example of an OpenCart shopfront, visit the Gaelic Books Council, who have one.
It does what you’d expect it to do and for most other things, there’s a load of extensions available to jazz it up.
The Gaelic language pack is now freely available too and you can download it here. Please note that this is a partial language pack which gives you the shopfront (i.e. what the customers see) in Gaelic. The “backend” (what the admins see) has not yet been translated.
As for OpenCart itself, that is available here. If you have any technical questions about installing and operating OpenCart, the communty forum is a good place to start.