ruby on rails - How to call specific action on drop down selected change event in rails3.1 -

On my page there is select_tag and this is the language store in the drop down. Now I change all the messages according to the selected language in the drop down Want to For this, I need to take action on the selection changes. So how do I call it?

Thanks, Fine

Maybe drop down a form, when drop Down change uses Javascript to submit the form.