Hide language selector if only one language is available

Don't add the language selector to the user interface if there is only
one valid language present in the application's configuration data.

This change also prunes empty languages and the special 'qqq' language
from the list of available languages. Finally it deletes the empty
translation files that were left from I097a4dd.

Change-Id: I4d4f2d736fc17e239bb95802437cb42d7070b45d