How to translate a node without creating a new node? I have translation enabled for the node type page, settings " Require language (Do not allow Language Neutral)." and " Normal - All enabled languages will be allowed".

However, when I'm creating and translating a node, it creates a new node instead of translating just the fields and storing the content in $node-&gt;body["en_US"][0]. How do I fix that?
That is the way in which the Internationalization module works, when you go to translate a node the module create a copy in another language, if you want one node with the fields transalted you must look at the Entity Translation module.

You can read more in this in Node translation vs. Entity (field) translation