Computer languages in langage tag

I'm astonished about absence of computer languages in HTML lang tag. As 
I can see You are using RFC 5646 
<http://www.rfc-editor.org/rfc/rfc5646.txt> language specification which 
aims only for human languages. Unfortunately, I don't see a point of 
separating lang and code tags. The only difference between this two are 
target user and tighter syntax in computer ones. My goal is to make 
information in my CMS best structured and described for uses in semantic 
web. Furthermore, I believe we can learn computers understand human 
languages in the future. Firstly, could You lighten me up the reasons of 
distinguishing them? Secondly, is there any way to treat both groups in 
similar manner in standards friendly way?