Translation Load More button

Hi, I have recent posts on homepage. Max. posts is 3 and after that the 'Load More' button is there. I would like to have this button in Dutch language. I downloaded the nl-NL.po file and opened it with poedit pro software but can not add the string to the translations list. Did I try it the right way or is there another way to realize the translation for this button? Thank you so much, Dirk