Enable placeholder translation for exposed filters
I'll post the solution I worked out just in case someone might need it. Using the hook_form_alter() function: 

function YOUR_THEME_form_alter(&amp;$form){
  if($form['#id'] == 'your_form_id'){
    foreach ($form['#info'] as $filter_info) {
        $filter = $filter_info['value'];
        if ($form[$filter]['#type'] == 'field_type' &amp;&amp; $filter == 'field_title') {
            $form[$filter]['#attributes']['placeholder'] = t('your_placeholder');
        }
    }
}