How can I hide the active language in the language switcher block?
The links generated by the Language API are alterable via hook_language_switch_links_alter(), so you can do this:

/**
 * Implements hook_language_switch_links_alter().
 */
function MYMODULE_language_switch_links_alter(array &amp;$links, $type, $path) {
  global $language;

  unset($links[$language-&gt;language]);
}