Translate message from tabledrag.js
Drupal loaded only the needed strings on every page which we are included. 
Those strings are added in javascript itself.

I think this is fixed by across the script files before they are actually added to the page.

So, you should be able to translate that string into the translate interface.

For more help, You can see this link,

https://www.drupal.org/node/323109

Hope it will be helpful.