One of the more subtle improvements in 8.1 is the addition of a few new UI languages which are:-
Afrikaans (af-ZA)
Basque (eu-ES)
Galician (gl-ES)
Hausa (ha-Latn-NG)
The full list for comparison across 8.1, 8.0 and 7.1 is here:-
http://msdn.microsoft.com/en-us/library/windowsphone/develop/hh202918(v=vs.105).aspx
In The Hand Ltd 