Adds a language.
$langcode: The language code of the language to add.
function addLanguage($langcode) {
$edit = array(
'predefined_langcode' => $langcode,
);
$this
->drupalPost('admin/config/regional/language/add', $edit, t('Add language'));
drupal_static_reset('language_list');
$this
->assertTrue(language_load($langcode), t('Language %langcode added.', array(
'%langcode' => $langcode,
)));
}