Chinese characters cannot be displayed correctly in Toad

The character set of my database is AMERICAN_AMERICA.WE8ISO8859P1,
and I create the system environment variable NLS_LANG with the value AMERICAN_AMERICA.WE8ISO8859P1.
But in toad ,chinese characters in tables turn out to be some wierd symbols,like »Ý°².
In sqlplus these tables display correctly.Any solution to resolve this problem?