Hi,
I use SIGPRO and the Popup engine Slimbox2 (jQuery based).
I have been edited the file: plugins/content/jw_sigpro/includes/js/jquery_slimbox/src/slimbox2.js

Like this:
counterText: "Bild {x} av {y}", // Translate or change as you wish, or set it to false to disable counter text for image groups

Why doesn't it affect the counter text in the pop-up window then?
Am I totally in the wrong file or is it something else playing games with me?

As I can't remove this I let anyone know that it was solved after searching more deep into the forum.
The file to edit is:
includes/js/jquery_slimbox/js/slimbox2

Search for counterText and then just edit the string to your language.

Could you be more specific please? Please provide us with a link to your site.

Sorry if I was unclear. This one was solved. I found the answer here in the forum.