We have repeated reports of data loss - translations that were in progress and disappeared. Fixing T106424 resolved some of these issues, but probably not all.
While it would probably be too challenging to save every single change to a translation, like Etherpad or Google Docs, it shouldn't be too hard to auto-save an article multiple times and keep the saved translations at least until publishing. In this case, if a bug causes paragraphs from a good in-progress translation to be deleted or overwritten by an empty auto-saved version, it will be at least possible to restore a previously saved revision.
Something like this is done in WordPress - it auto-saves a post that is being edited every minute or so.