How can I set LANG to ASCII?

I'm accessing an Ubuntu machine using PuTTY, and using gcc.

The default LANG environment variable on this machine is set to en_NZ.UTF-8, which causes GCC to think PuTTY is capable of displaying UTF-8 text, which it doesn't seem to be.Maybe it's my font, I don't know - it does this:

foo.c:1: error: expected â=â, â,â, â;â, âasmâ or â__attribute__â at end of input

If I set it with export LANG=en_NZ, then this causes GCC to behave correctly, I get:

foo.c:1: error: expected '=', ',', ';', 'asm' or '__attribute__' at end of input

but this then causes everything else to go wrong. For example

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

I've trawled Google and I can't for the life of me find out what I have to put in there for it to just use ASCII. en_NZ.ASCII doesn't work, nor do any of the other things I can find.