a problem about acroread

jamesxuruo

my linux is RH9.0 english
i try to install acroread.when i run acroread :
first, i go to the directory i installed :/usr/local/Acroread5/bin
and then type "./acroread", the terminal tells me that:
Walling: charset "UTF-8" not supposed, using "ISO8859-1"
i try to know my env:
echo $LANG
the terminal tells me:en_US.UTF-8
and i try to change my env: unset LANG
then i can use my acroread
but i don't know what i have done
so please tell me why!
thx