It is difficult to answer this question without knowing exactly which version of Checkbox you are using. My response assumes you are using the current release of the product, version 4.4.1.14.
1. Both the header and footer text support multi language support. On the EditHeader.aspx page you should see a dropdown list in the upper right hand corner which lists the available languages. Select the language you would like to edit, make your changes, save them and repeat for as many languages as you would like.
2. I do not believe it is possible to control which style/page template is used based on the survey language. I will add this request to the development teams internal tracker.
3. At this time the application text is controlled by your selection on the login page. If you have configured more than one application language you will need to select which you would like to use when logging in.
For more information on MLS support I would suggest reviewing our training page (
http://www.prezzatech.com/training/), there are a couple of videos and a quick start guide on the subject.