Can't translate 'select option'

Hi, I checked a previous post by a user that had my exact same problem but the solution wasn’t public so I have to post the question again. In the Advanced Search how do I translate the string ‘Select option’? In wp-content/languages I’ve created a folder named geodir_advance_search_filters and in the .po file I’ve translated both lines ‘Select option’ and ‘Select Option’ (there’are two of them) but it seems like my changes get ignored. Note that in the same file I changed the word ‘Advanced’ into my language and it perfectly worked so I’m sure that file name, path, folder name and so on are all correct. I’m using GD with Whoop theme.