Combine "folder as GET parameter" and "subdomain as GET parameter" - regex

Question

I have a site that rewrites path after domain to a page GET parameter.
##REWRITING DIRECTORIES TO GET PARAMETERS
RewriteBase /
#Ignore all real directories (do not rewrite them)
RewriteCond %{REQUEST_FILENAME} !-d
#Also do not rewrite real files
RewriteCond %{REQUEST_FILENAME} !-f
#For everything else, index.php should fetch the proper content
RewriteRule ^([^/]*)$ index.php?page=$1 [QSA,L]
##This means:
#example.com/help
#~becomes~
#example.com?page=help
The site uses multiple languages and so far, I've been using cookies to set and remember the language for the user. While the convenience for the user is disputable, this is definitely not convenient for the SEO.
I need to rewrite [a-z]{2}\.mydomain\.xx to index.php?lang=$1 so that user will be always on en.domain.com for example. There are examples to do this, however I'm still confused about how the rewrite engine works and I don't know how should I combine my new rules with the old ones:
##Language rewrite
#Copypasted. Didn't understand
RewriteCond %{HTTP_HOST} ^([a-z]{1,2})\.domain\.xx
RewriteRule ([a-z]{1,2})\.domain\.xx index.php?lang=$1 [QSA,L]
How can I get en.domain.com/help turn in index.php?page=help&lang=en?

Answer 1

How can I get en.domain.com/help turn in index.php?page=help&lang=en
You can use:
RewriteEngine On
RewriteBase /
#Ignore all real directories (do not rewrite them)
RewriteCond %{REQUEST_FILENAME} !-d
#Also do not rewrite real files
RewriteCond %{REQUEST_FILENAME} !-f
#For everything else, index.php should fetch the proper content
RewriteCond %{HTTP_HOST} ^([a-z]{1,2})\.domain\.xx$ [NC]
RewriteRule ^([^/]+)/?$ index.php?lang=%1&page=$2 [QSA,L]
Reference: Apache mod_rewrite Introduction