When a user first comes to the website, their content language is selected and stored in a cookie. You can specify for every domain and domain alias which culture should be used by default.
Go to Site Manager -> Sites and edit site Corporate Site. On the General tab, you can see the Default visitor culture field. You can choose either some particular language that will be used by default or you can choose the option (Automatic) that displays the content based on the preferred language of visitor's web browser (in Internet Explorer, you can set the default language in Tools -> Internet Options -> Languages). It automatically selects the nearest content culture that is available for the given website.
Language selection based on the domain
You can configure the system to use different default languages based on the current domain. If you use the following domains:
|•||example.com (main domain)|
|•||example.de (domain alias)|
|•||example.fr (domain alias)|
you need to set the default cultures English, German and French to the domains/domain aliases (respectively). Now, when a visitor comes first to e.g. example.fr domain, the content is automatically displayed in French.