language: fixed test breakage

Missed some adjustments in the move from en-US-x-posix to
en-US-u-va-posix.

Fixes #12987.

Change-Id: Ie422598c955359556b4d0d244062b0bf267c022c
Reviewed-on: https://go-review.googlesource.com/16011
Reviewed-by: Hyang-Ah Hana Kim <hyangah@gmail.com>
3 files changed