First of all, add different languages to your account. Read more in this article.
Now that we have the multiple language settings, we can translate our story.
On the Stories overview page a new translate option will be available:
Clicking on Translate will duplicate the given story, link it the original version and redirect you to the editor where you can start translating your story. When you are ready you can continue to summary and select the language you translated the story to:
When the story needs to be translated by a co-worker or external translator, just go to summary, change the language, and then invite a user (co-worker or translator) to translate the story.