Well, It appears that the Translation plugin is not ready for use, particularly if you are using Hogfather.
I just experienced the problem after I added
<?php
$translation = plugin_load('helper','translation');
if ($translation) echo $translation->showTranslations();
?>
to
lib/tpl/bootstrap3/main.php
lib/tpl/dokuwiki/main.php
And the wiki instantly disappeared.
I would like to know how I can setup for and get started with Language translations, given this situation.