What type of alert are you excpecting to receive?

To me it seems like an implementation issue. It could be that the attribute which defines the users-language is not set when sending the request to the dispatcher. It is hard to tell exactly without looking at the code. Perhaps you could add a default message in your if statements which will be prin...

In the past i have used succesfully a jquery AJAX request to post data to the Sling Servlet, as shown in the following link.http://helpx.adobe.com/experience-manager/using/custom-sling-servlets.html