These files are not meant to be published or anything, they are meant to exchange data between tools. XLIFF files are by design bilingual. An XLIFF file contains both the source and target text as well as segment status if the translation is completed. It always contains the source text no matter what the translation status is. For example, it is possible to import a partially translated XLIFF file in a tool and complete the translation, reusing the partial translation and segment status.
It is possible to export an XLIFF file at any time during the translation process in Smartcat.