Lang parameters in url rewriting - apache

Question

Some times now I'm around my htaccess and no way to get what I want...
I'd like to rewrite as followings :
http://www.mydomain.com/trunk/public/lang/ => http://www.mydomain.com/trunk/public/?l=lang
http://www.mydomain.com/trunk/public/lang/profile => http://www.mydomain.com/trunk/public/profile?l=lang
http://www.mydomain.com/trunk/public/lang/user/45 => http://www.mydomain.com/trunk/public/user/45?l=lang
...
Any idea how to do that?
--------EDIT-------
My htaccess actually looks like :
<IfModule mod_rewrite.c>
RewriteEngine On
#Transform lang into get parameter
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(fr|en)/$ ?l=$1 [L,QSA]
#Transform lang into get parameter
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(fr|en)/(.+)$ $1?l=$2 [L,QSA]
#This last condition enables access to the images and css folders, and the robots.txt file
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond $1 !^(index\.php|public|images|assets|robots\.txt|css)
RewriteRule ^(.*)$ index.php/$1 [L]
</IfModule>
Results :
http://www.mydomain.com/trunk/public/lang/ gives a bonfire 404 error (it tries to load "lang" module)
http://www.mydomain.com/trunk/public/lang/profile gives a server 404 error
http://www.mydomain.com/trunk/public/profile works
http://www.mydomain.com/trunk/public/profile?l=fr works
I have managed to set the default domain destination in the trunk/public folder via an htaccess placed in a the trunk parent directory

Answer 1

Insert these 2 rules in your /trunc/public/.htaccess file:
RewriteEngine On
RewriteBase /trunc/public/
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^([^/]+)/?$ ?l=$1 [L,QSA]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^([^/]+)/(.+)$ $1?l=$2 [L,QSA]