Prepare a language code list for unused predefined languages.
function language_admin_predefined_list() {
$languages = language_list();
$predefined = LanguageManager::getStandardLanguageList();
foreach ($predefined as $key => $value) {
if (isset($languages[$key])) {
unset($predefined[$key]);
continue;
}
$predefined[$key] = t($value[0]);
}
asort($predefined);
return $predefined;
}