Natty (Ubuntu 11.04) alpha 1 without ja_JP as default language

As declared on the first day of the year, from the end of last year 2010, started testing Natty (Ubuntu 11.04) alpha 1. To use English environment with full ja_JP, wanna set en_US as default language. but...

$ locale
locale: Cannot set LC_MESSAGES to default locale: No such file or directory
locale: Cannot set LC_ALL to default locale: No such file or directory
LANG=en_US.UTF-8
LANGUAGE=en_US.UTF-8:en
LC_CTYPE="en_US.UTF-8"
LC_NUMERIC="en_US.UTF-8"
LC_TIME="en_US.UTF-8"
LC_COLLATE="en_US.UTF-8"
LC_MONETARY="en_US.UTF-8"
LC_MESSAGES=en_AG.utf8
LC_PAPER="en_US.UTF-8"
LC_NAME="en_US.UTF-8"
LC_ADDRESS="en_US.UTF-8"
LC_TELEPHONE="en_US.UTF-8"
LC_MEASUREMENT="en_US.UTF-8"
LC_IDENTIFICATION="en_US.UTF-8"
LC_ALL=

In detail, lc_messages is wrong:

$ locale
[...]
LC_MESSAGES=en_AG.utf8
[...]

and lc_all is empty:

$ locale
[...]
LC_ALL=

soon after the installing Ubuntu 11.04 alpha 1 on VirtualBox.