Question

How can be this

http://some-url.com/?lang=en

rewritten to this:

http://en.some-url.com ???

via mod_rewrite?

Answer 1

You could define all possible languagespecific subdomains as ServerAlias in the VirtualHost-configfile of some-url.com and add following rewriterule

RewriteEngine On
RewriteCond %{HTTP_HOST} ^some-url\.com$ [NC]
RewriteCond %{QUERY_STRING} lang=(.*)$
RewriteRule . http://%1.some-domain.com/? [R=301,L] 

In your serverside script you can get the actual language by checking SERVER/CGI variable called HTTP_HOST (in php this would be $_SERVER['HTTP_HOST'] while in ColdFusion this would be #CGI.HTTP_HOST#)