hyper link not working using SSI on web page

I have already added following SSI script, if I run index-cht.html, it will show "Eng" on the top right corner, if i run index.html, it will show "Chinese", it is fine, but it cannot give the hyper link on "Eng" and "Chinese", I post the following script, is it something wrong? Thanks.

div id="Language">
<!--#set var="fileName" value="$DOCUMENT_NAME" -->
<!--#if expr="$fileName = /index-cht.html/"-->
<a href="/index.html" class="english">Eng</a>
<!--#else -->
<a href="/index-cht.html" class="chinese">Chinese</a>
<!--#endif-->
</div>