Hello Catherine Labat
Welcome to the Tableau Community Forums.
Thank you for the post regarding Xiti. I see that Xiti is a Web Analytics data collection and analysis too. Unfortunately, we are not familiar with this platform and its capabilities.
I spent a few minutes researching the Xiti site and located this page: http://www.atinternet.com/en/product/web-analytics/data-exploration/ . Based on the information on this site, it appears that both CSV and Excel files are the potential export options that would be usable with Tableau.
In addition, you may wish to request that the Xiti platform be added as a native Tableau data source by utilizing the Tableau Community Ideas section here: Space: Ideas | Tableau Support Community
Note that I have updated the original French post to point to this post as well.
Regards and welcome again.