Hi,
I solved this by modifying my (custom) template. I created two files ...
navigation.de.html
navigation.en.html
... and then replaced by default sidebar in the template's main.php by this PHP code
<div class="navigation">
<?PHP
$lngNav = dirname(__FILE__).'/navigation.'.$conf['lang'].'.html';
if (!file_exists($lngNav)) {
$lngNav = dirname(__FILE__).'/navigation.en.html';
}
@include($lngNav);
?>
</div>
Is not perfectly elegant, but works fine.