Polylang

polylang_stuff.php

<?php
/* language switcher */
  $translations = pll_the_languages( array(
    'show_flags' => 0,
    'hide_if_no_translation' => 1,
    'hide_current'=> 1,
    'raw' => 1)
  );
  
  if (count($translations) > 0){
    $lang_switcher_text = '';
  
    foreach ($translations as $translation){
      $lang_switcher_text .= 
        '<li><a href="' . $translation['url'] . '">' . 
          '<img src="' . $translation['flag'] . '" /> ' . $translation['name'] . 
        '</a></li>';
    }
  
    $lang_switcher =
     '<div id="language-switcher-header" class="row"> ' .
        '<ul>' . $lang_switcher_text . '</ul>' .
      '</div>';  
  }
  
  echo $lang_switcher;
?>

<?php
/* get corresponded translated post id (works with post_types too) */
  global $post;
  $polylangPostID = pll_get_post($post->ID);
  $translatedPost = get_post($polylangPostID);
  $title = apply_filters( 'the_title', $translatedPost->post_title );
  $content =  apply_filters( 'the_content', $translatedPost->post_content );
?>