You have to export your captions directly into an MS Word document from the Captivate project itself using File > Export > Project Captions and Closed Captions. Don't use the XML export.
Then you must change NOTHING about that CPTX file whatsoever between the time you to the export and the time your translated document comes back to you. Changing anything in the CPTX risks an unsuccessful import. So mothball the CPTX and take a copy of that file if you will be needing an original language version of it as well.
When you get your translated MS Word doc back, hopefully the translator has ONLY done changes to the column that is indicated to be the translated one, and has made no changes to the other column that contains the original language. Then you should be able to import the captions and closed captions by going to File > Import > Project Captions and Closed Captions.