If you have chosen to the multiple domain path to implement your multilingual sites, either on your own or based on my previous post, Single Domain vs. Multiple Domain Implementation, the good news that it’s more configuration than development, with the bulk of it being done inside the web.config.
This was tested on Sitecore v6.1, so please perform ample testing when working with other versions.
Default Web.config Sites Section
<sites>
<site name="shell" ... />
<site name="login" ... />
<site name="testing"... />
<site name="admin" ... />
<site name="service" ... />
<site name="modules_shell" ... />
<site name="modules_website" ... />
<site name="website" ... />
<site name="scheduler" ... />
<site name="system" ... />
<site name="publisher" ... />
</sites>