Hello,
You can use this code
<?php if (isloggedin() or isguestuser()) { ?>
<ul id="language">
<li><a href="<?php echo $CFG->wwwroot;?>?lang=en">English</a></li>
<li><a href="<?php echo $CFG->wwwroot;?>?lang=ja_kids;">日本の</a></li>
</ul>
<?php }else{?>
<?php }?>
on page header in frontpage.php and general.php.