Translate field in members directory

Hi,
Thank you for this amazing plugin.
I have a translation issue:
I am using Polylang for translation and I have already read all your docs about translation. I have created different forms, one for each language and put the shortcode in translated pages. The problem is when I create a members directory with filters, I can only choose fields from a single language, so, for custom fields, the placeholder is not translated in frontend. The custom fields is a drop down and I have translated title, label and placeholder, but of course the meta key is and must be the same. So the question is, how can I translate drop down placeholder in members directory?

Thank you
Rick