Depending on how you plan to do the translation and how your InDesign document is set up, the simplest approach might be to export the individual stories as RTF files, which will retain all your stylesheet information. The translations can be done using the RTF files then imported back to a copy of the original InDesign file using 'File > Place' with the cursor in an empty text frame. This is how I normally approach a project like this. The down side is that you will inevitably end up with a great deal of copyfitting work to compensate for the different lengths of text in each language.
Exporting as XML requires you to first set up the XML structure in InDesign, which can be a tedious process if your document is large and complex. The advantage is that you can recreate the entire document from the XML using a template. I would only consider this workflow if you have a large number of translations to do and the tools to work easily with the XML data once it's exported. James Malvaid's excellent "A Designer's Guide to Adobe InDesign and XML" is your reference for the techniques you'll need.
If this is a workflow you expect to be using on a continuing basis with fixed number of staff translators, you might find that using InCopy will work out best in the long run.