Polylang — display flag or language code for term or post

frontend-functions.php

<?php

function polylang_display_language_code_for_object($type = 'post', $id = null) {

  $output = '';
  
  if ( function_exists('pll_get_post_language') && function_exists('pll_get_term_language') ) {

    // language slug
    $slug = '';

    if ( $type === 'post' ) {
      $slug = pll_get_post_language( $id );
    }
    if ( $type === 'term' ) {
      $slug = pll_get_term_language( $id );
    }
    
    if ( $slug ) {
      $flag = file_get_contents( WP_PLUGIN_DIR . '/polylang/flags/' . ( $slug === 'en' ? 'us' : $slug ) . '.png' );

      if ( $flag ) {
        $output .= ' <img alt="' . __( 'Flag', 'site' ) . '" src="' . 'data:image/png;base64,' . base64_encode( $flag ) . '">';
      } else {
        $output .= ' (' . $slug . ')';
      }
    }
  }

  return $output;
}