Strange mv -vf output under en_US.UTF-8

My mv -vf output is very strange:

cd /tmp
touch xx yy

$ mv -vf xx yy
â -> â

$ env | grep ^LANG
LANG=en_US.UTF-8

The correct output should be:

$ mv -vf xx yy
'xx' -> 'yy'

This is from,

$ env | grep ^LANG
LANG=C

If I set LANG=C then the mv -vf output is correct again.

How is that? Would there be any fix?

$ lsb_release -a 
No LSB modules are available.
Distributor ID: Ubuntu
Description:    Ubuntu 15.04
Release:        15.04
Codename:       vivid