I don't think you even have to create a menu item. If you've installed Xmap, all you have to do is go to Components-->Xmap and click the Xml Sitemap link. Copy the URL from the resulting page to use in your submission to Google. I've never used multiple languages, so I have no clue about that.
Hi Tylor thank you for your message. I am still not sure on what is the best way to use Xmap specially on a multilingual site so if any of you have any idea thank you very much.