can't set the locale; make sure $LC_* and $LANG are correct problem in Ubuntu 11.10 (32 bits)

I had this problem after installing Ubuntu 11.10 (32 bits). From a terminal, every time I executed some commands (apt-get install, update, man xxx, etc), some locale warnings appeared, like this one

can't set the locale; make sure $LC_* and $LANG are correct

Also this error messages were shown:
Cannot set LC_TYPE to default locale: No such file or directory

I solved the problem by adding in /etc/environment the following line
LC_ALL="en_US.utf8"

and then rebooting the system.

With this line, everything worked just fine. No more errors/warnings at the console!!