Additionally, for XML schema correctness, convert ISO-639-2 language
tags (three-letter codes) to ISO-639-1 tags (two-letter codes) when
possible. This follows BCP-47, which says to always use the shortest
language tag when there are multiple possibilities.
b/18613148
Change-Id: I120fb7b42ac4da5feb4ca046bba93d9e58acd7a9
Joey Parrish