RewriteRule: "using more than one path"

Hard to explain in the subject what I need.

I have these rules inside my httpd.conf:

RewriteRule ^/articles/([0-9]+)/(en|it).htm$ /src/articles.php?lang=$2&id=$1 [T=application/x-httpd-php,L]
RewriteRule ^/articles/(en|it).htm$ /src/articles.php?lang=$2 [T=application/x-httpd-php,L]

The first is used to convert:
/articles/11/it.htm -->> /src/articles.php?lang=it&id=11

the second is used to convert:
/articles/it.htm -->> /src/articles.php?lang=it

I use articles.php to view the article if $id is not empty,
to display the list of articles if $id is empty.

I'm asking if there is a way with regular expression to put these two rules inside one.
I tried something like this:

^/articles/(([0-9]+)/(en|it).htm)|((en|it).htm)$

but with an orrible output.

Is it possible or is it better to have two rules as I wrote?

Just don't use ([0-9]+), use ([0-9]*) instead, so that id can be empty.
You also should add a catch-all RewriteRule to display error message when it matches something under ^/articles(.*) but not your preceding Rule so that Apache knows what to do instead of throwing you with weird errors.