Unable to convert correct characters from gb2312 to utf8

Issue

• In the System , it is not able to covert the correct characters. For example, the original file charatercs is gb2312 or gb18030 gbk, run the below command:

iconv -t utf-8  example.txt -o  utf.txt 

There some error is as the below:

iconv : unkown 170  invalid  input 

The system Language environment is :

echo $LANG
LANG=zh_CN.gb2312

How to fix it ?