Redirect to language version site using Url Rewriting IIS7

Question

When user types www.domain.com he should be instantly redirected to his language version or if he have no language specified in his browser, to default language 'en'.

The problem is to find the good rule to redirect the user to default language when he don't specify any. I'm trying the following expression without success:

<rule name="www.domain.com" stopProcessing="true">
   <match url="www.domain.com$" />
   <action type="Redirect" url="/en/" />
</rule>

It simply doesn't anything. I'll appreciate any help.