invalid locale

To see all available language packs, run:

apt-cache search "^language-pack-[a-z][a-z]$"

To disable this message for all users, run:

sudo touch /var/lib/cloud/instance/locale-check.skip

And, eventually I did
vim ~/.bashrc

export LC_ALL="en_US.UTF-8"

then

export LC_ALL="en_US.UTF-8"
locale-gen en en_US en_US.UTF-8
dpkg-reconfigure locales