There are two out of the box Ektron server controls for selecting and using Site Langauge: the LanguageSelect and LanguageAPI server controls. They can be found here.
The issue is that these controls are not 3-tier compatible. If you want to develop a language selection control, it will have to be with our framework APIs.
Please use the framework APIs to create you own user control for template use. The sample of the API is located in our templates section here.
<%= heading %>