I see, However it seems rather complicated to have to deal with .po files especially as I use WPML for all my translations and do not want to mess something up.
Is there a way to use WPML to change that string?
You say it is easy, but really, easy would be if you provided a textfield for changing that string in the promo popup section of the theme settings. This would take your developers 5 minutes to fix, but in 3 years it has not been done. I cannot be the only one requesting this?