To enable the search engine friendly URL codification try the following:

Save the following content in a file called ".htaccess",
then you should enable the following flag in the "config.inc.php" - file:

name of the flag in "config.inc.php": 
$rewriteEngine = "on";
content of ".htaccess": 
AddType application/x-httpd-php .html
Options +FollowSymLinks
RewriteEngine on
RewriteRule index_(.*)_(.*)_(.*)\.html index.html?lang=$1tp=$2&page=$3
RewriteRule index_(.*)_(.*)_(.*)\.php index.php?lang=$1tp=$2&page=$3
The first line of this file (AddType application/x-httpd-php .html)
gives the direction to the webserver to parse also .HTML files
so you should be able to use the "index.html" file instead of "index.php"!