Different taxonomy term title for menu and term page
You can use drupal_set_title() with implementing hook_preprocess_page().

/**
 * Implements hook_preprocess_page().
 */
function mymodule_preprocess_page(&amp;$variables) {
  $langcode = $variables['language']-&gt;language;
  $term = menu_get_object('taxonomy_term', 2, $langcode);
  if (!empty($term)) {
    drupal_set_title($term-&gt;custom_field[$langcode][0]['value']);
  }
}


menu_get_object() may not work because some module may override the menu entry taxonomy/term/% as mentioned by mxh.

If you want more robust way to retrieve the term object. Please use below snippet.

if (arg(0) == 'taxonomy' &amp;&amp; arg(1) == 'term' &amp;&amp; arg(2)) {
  $term = taxonomy_term_load(arg(2));
}
if (isset($term) &amp;&amp; !empty($term)) {
  // code.
}