Two chars language name in drupal's language switcher

template.php

/**
 * theme_link for local block.
 *
 * Get language code as language switcher link (two chars)
 *
 * @param type $variables
 * @return type
 */
function THEME_links__locale_block($variables) {
  foreach ($variables['links'] as $key => $value) {
    $lang = $value['language']->language;
    $variables['links'][$key]['title'] = drupal_strtoupper($lang);
  }
  return theme('links', $variables);
}