Output ctools_modal_form_wrapper() with translatable items in the form i have translation strings already for this form.
if i output it with: 

  return drupal_get_form('user_login');


then the translation works

but if i render it for the modal form then the translation doesn't work.

return ctools_modal_form_wrapper('user_login', $form_state); with translatable items


so how can i enable the tranlation for the ctools_modal_form_wrapper also?
This is an open issue for ctools modal_form and is in need of some more data / feedback to push the issue forward. The specific bug is called out here and appears to be related to the language header that is used in the modal form window:

https://www.drupal.org/node/2160293

There is a potential patch for this here:

https://www.drupal.org/node/2245123