Hello Hector,
Thanks for your question,
Since his original architecture (CMS), xili-language use built-in taxonomy features of WP and keep original characteristics of posts (page or article or since 3.0 custom post).
So, to call a post with his only one affected language, only the permalink (or his short ID ?p=, ?page_id=) is used – no query tag lang –
The language taxonomy with query tag (lang) is used only – very seldom- when sub-selecting posts for one language in home or in a category.
If you visit https://dev.xiligroup.com or http://multilingual.wpmu.xilione.com/ or lot of sites using xili-language trilogy you can see that this query tag is used currently in menu or in languages list when a category is displayed.
A template tag exists also to generate link a post to his translation/adaptation in another lang when displayed as a single. and lots of not-visible feature to do very original browsing…
If you need more professional infos or comparison with other WP plugins, please contact me here https://dev.xiligroup.com/?page_id=10
Best regards,
2014-xili