How to add custom field to custom taxonomy in 4.4

You can implement this in two ways to add meta boxes through plugin or wordpress predefined hooks

https://wordpress.org/plugins/taxonomy-metadata/

  **OR**

Add the following code in functions.php in your theme

function mj_taxonomy_add_custom_meta_field() {
        ?>
        <div class="form-field">
            <label for="term_meta[class_term_meta]"><?php _e( 'Add Class', 'MJ' ); ?></label>
            <input type="text" name="term_meta[class_term_meta]" id="term_meta[class_term_meta]" value="">
            <p class="description"><?php _e( 'Enter a value for this field','MJ' ); ?></p>
        </div>
    <?php
    }
add_action( 'product_cat_add_form_fields', 'mj_taxonomy_add_custom_meta_field', 10, 2 );





 function mj_taxonomy_edit_custom_meta_field($term) {

        $t_id = $term->term_id;
        $term_meta = get_option( "taxonomy_$t_id" ); 
       ?>
        <tr class="form-field">
        <th scope="row" valign="top"><label for="term_meta[class_term_meta]"><?php _e( 'Add Class', 'MJ' ); ?></label></th>
            <td>
                <input type="text" name="term_meta[class_term_meta]" id="term_meta[class_term_meta]" value="<?php echo esc_attr( $term_meta['class_term_meta'] ) ? esc_attr( $term_meta['class_term_meta'] ) : ''; ?>">
                <p class="description"><?php _e( 'Enter a value for this field','MJ' ); ?></p>
            </td>
        </tr>
    <?php
    }

add_action( 'product_cat_edit_form_fields','mj_taxonomy_edit_custom_meta_field', 10, 2 );



function mj_save_taxonomy_custom_meta_field( $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_product_cat', 'mj_save_taxonomy_custom_meta_field', 10, 2 );  
add_action( 'create_product_cat', 'mj_save_taxonomy_custom_meta_field', 10, 2 );