Drupal API - How to add field translation for label

gistfile1.php

<?php
$entity = 'node';
$field_name = 'employee_first_name';
$bundle = 'employee';
$lang_code = 'fi';
$value = 'Nimi';

// get field instance

$instance = field_info_instance($entity, $field_name, $bundle);

// get instance of i18n_field_instance

$field_instance = i18n_object('field_instance', $instance);

// get textgroup and context

// field:$field_name:$bundle:label
list($textgroup, $context) = i18n_string_context('field:employee_first_name:employee:label'); 

i18n_string_textgroup($textgroup)->update_translation($context, $lang_code, $value);