Fix F/C in TTS settings

This is an attempt to fix uncaught MissingResourceException
that would be thrown if default language of selected engine is
set to a locale that has no 3-letter country/language code.

Please see https://code.google.com/p/android/issues/detail?id=63122

Change-Id: Iccb2a55f5f7a97819310fd888559650fe7febe4a
Signed-off-by: Shuhrat Dehkanov <k@efir.uz>