The url called:
http://server.com/l/eng/a/emailform

The url it should transform into:
http://server.com/index.php?lang=eng&action=emailform

The rewrite code in .htaccess:
<IfModule mod_rewrite.c>
    RewriteEngine On
    RewriteBase /
    RewriteCond %{THE_REQUEST} /l/(.*)/a/(.*)/\?(.*)
    RewriteCond %{REQUEST_URI} !/index\.php$
    RewriteRule .   /index.php?lang=/%1&action=%2&%3   [QSA,L]
</IfModule>

The error in the apache log:
File does not exist: /home/user/public_html/l

The error in the browser:
The requested URL /l/eng/a/emailform was not found on this server.