Multilanguage site with specific language subdomains

I want to make a multilingual site with more subdomains. Lets say i have example.com the domain. I want to have this on 3 languages : english, french and romanian. I have 3 subdomains named :

1. ads.example.com
2. annonces.example.com
3. anunturi.example.com

I created a directory where is pointed all this subdomains where i have a joomla multilanguage installed. How can i do activate every subdomain to be pointed at specific language?