Files Together v.1.5 comes with English (default) German, French and Spanish settings. To set the default language you must be in the admin group.  If so, proceed as follows:

• Click on Tools \ Options

   

The Options screen will appear.  Ensure that you are in the 'Languages' tab from the tab group.

    

• Select either English or Japanese from the Set default language drop down box.
• Click on Update default Language

You can also add in new languages and make up your own translations with no exra coding involved.