Adicionar novo campo (custom field) a uma taxonomia no WordPress (Incluir esse código no functions.php)Nas action_hooks, no lugar de "category" é só incluir o slug da sua taxonomia :)

add-field-to-taxonomy.php

<?php
// Add term page
function taxonomy_add_new_meta_field() {
  // this will add the custom meta field to the add new term page
  echo '
    <div class="form-field">
      <label for="term_meta[custom_term_meta]">Example meta field</label>
      <input type="text" name="term_meta[custom_term_meta]" id="term_meta[custom_term_meta]" value="">
      <p class="description">Enter a value for this field</p>
    </div>
  ';
}

add_action( 'category_add_form_fields', 'taxonomy_add_new_meta_field', 10 );







// Edit term page
function taxonomy_edit_meta_field($term) {

  // put the term ID into a variable
  $t_id = $term->term_id;

  // retrieve the existing value(s) for this meta field. This returns an array
  $term_meta = get_option( "taxonomy_{$t_id}" );
  $value = esc_attr( $term_meta['custom_term_meta'] ) ? esc_attr( $term_meta['custom_term_meta'] ) : '';

  echo '
    <tr class="form-field">
    <th scope="row" valign="top"><label for="term_meta[custom_term_meta]">Example meta field</label></th>
      <td>
        <input type="text" name="term_meta[custom_term_meta]" id="term_meta[custom_term_meta]" value="' . $value . '">
        <p class="description">Enter a value for this field</p>
      </td>
    </tr>
  ';
}

add_action( 'category_edit_form_fields', 'taxonomy_edit_meta_field', 10, 1 );







// Save extra taxonomy fields callback function.
function save_taxonomy_custom_meta( $term_id ) {
  if ( isset( $_POST['term_meta'] ) ) {

    $t_id = $term_id;
    $term_meta = get_option( "taxonomy_{$t_id}" );
    $cat_keys = array_keys( $_POST['term_meta'] );

    foreach ( $cat_keys as $key ) {
      if ( isset ( $_POST['term_meta'][$key] ) ) {
        $term_meta[$key] = $_POST['term_meta'][$key];
      }
    }

    // Save the option array.
    update_option( "taxonomy_{$t_id}", $term_meta );

  }
}

add_action( 'edited_category', 'save_taxonomy_custom_meta', 10, 1 );
add_action( 'create_category', 'save_taxonomy_custom_meta', 10, 1 );

Adicionar novo campo (custom field) a uma taxonomia (categoria, tag, etc) no WordPress.md

Adicionar novo campo (custom field) a uma taxonomia (categoria, tag, etc) no WordPress

Incluir esse código no functions.php.

Nas action_hooks, no lugar de "category" é só incluir o slug da sua taxonomia :)