go get github.com/axgle/mahonia

func ConvertToString(src string, srcCode string, tagCode string) string {

 srcCoder := mahonia.NewDecoder(srcCode)

 srcResult := srcCoder.ConvertString(src)

 tagCoder := mahonia.NewDecoder(tagCode)

 _, cdata, _ := tagCoder.Translate([]byte(srcResult), true)

 result := string(cdata)

 return result

}

str := "乱码的字符串变量"

str = ConvertToString(str, "gbk", "utf-8")

fmt.Println(str)