Translations are stored in the lang directory of the Xataface folder.  You'll notice files named: en.ini, fr.ini, and de.ini (English, French, and German respectively).  If you want your applicaiton to use the French translation, just add the following to your conf.ini file:

[languages]
fr="Français"

This will tell Xataface that your application is in French.  (The 'fr' is the 2-digit ISO code for French, and the 'Français' is what is displayed to the user).

Enabling multiple languages at once

If you want to enable multiple translations and allow the user to switch between them, you can do the following:

[languages]
en=English
fr="Français"
de="Deutch"

Xataface will try to detect which language is the user's preferred language and automatically show them the correct one.  The users can also click on the link to their language at the top of the Xataface application.