やったこと

・navi.phpに一行追加
・ja.phpに数行追加

navi.phpに一行追加

C:\xampp\security\htdocsのnavi.phpに一行追加。（C:\xampp\htdocs\xamppにもnavi.phpがあってこれで何時間もはまった）

navi.php

<td align="right" class="navi">
<a target=_parent class=n href="lang.php?de"><?php print $TEXT['navi-german']; ?></a><br>
<a target=_parent class=n href="lang.php?en"><?php print $TEXT['navi-english']; ?></a><br>
<a target=_parent class=n href="lang.php?es"><?php print $TEXT['navi-spanish']; ?></a><br>
<a target=_parent class=n href="lang.php?fr"><?php print $TEXT['navi-french']; ?></a><br>
<a target=_parent class=n href="lang.php?it"><?php print $TEXT['navi-italian']; ?></a><br>
<a target=_parent class=n href="lang.php?nl"><?php print $TEXT['navi-dutch']; ?></a><br>
<a target=_parent class=n href="lang.php?no"><?php print $TEXT['navi-norwegian']; ?></a><br>
<a target=_parent class=n href="lang.php?pl"><?php print $TEXT['navi-polish']; ?></a><br>
<a target=_parent class=n href="lang.php?pt"><?php print $TEXT['navi-portuguese']; ?></a><br>
<a target=_parent class=n href="lang.php?sl"><?php print $TEXT['navi-slovenian']; ?></a><br>
<a target=_parent class=n href="lang.php?zh"><?php print $TEXT['navi-chinese']; ?></a><br>
<a target=_parent class=n href="lang.php?jp"><?php print $TEXT['navi-japanese']; ?></a><p>

最後の行に
<a target=_parent class=n href="lang.php?jp"><?php print $TEXT['navi-japanese']; ?></a><p>
を追加している。

・ja.phpに数行追加

C:\xampp\security\htdocs\langのjp.phpに数行追加

ja.php

$TEXT['navi-languages'] = "各国語";

を

ja.php

$TEXT['navi-languages'] = "各国語";
$TEXT['navi-english'] = "English";
$TEXT['navi-german'] = "Deutsch";
$TEXT['navi-spanish'] = "Espanol";
$TEXT['navi-french'] = "Francais";
$TEXT['navi-italian'] = "Italiano";
$TEXT['navi-dutch'] = "Nederlands";
$TEXT['navi-norwegian'] = "Norsk";
$TEXT['navi-polish'] = "Polski";
$TEXT['navi-portuguese'] = "Portugues";
$TEXT['navi-slovenian'] = "Slovenian";
$TEXT['navi-chinese'] = "中文";
$TEXT['navi-japanese'] = "日本語";

にする。以上。