Hello,
I'm in the same situation i'm trying to translate Contact Form using Polylang.
I've tried f.lindenberg sugestion but not exactly since i'm not familiar with child themes instead i changed hardcoded in the test enviroment the recomended line from :
<input required="required" type="text" name="myname" placeholder="Your Name" class="form-control input-box" value="<?php if(isset($_POST['myname'])) echo esc_attr($_POST['myname']);?>">
in to :
<input required="required" type="text" name="myname" placeholder="<?php echo __('Your Name','zerif-lite');?>" class="form-control input-box" value="<?php if(isset($_POST['myname'])) echo esc_attr($_POST['myname']);?>">
but i cannot see any relevant or new field in the string translations fields of polylang plugin in order to translate it.
Any ideas?