How do I write out a text file in C# with a code page other than UTF-8?

using System.IO;
using System.Text;

using (StreamWriter sw = new StreamWriter(File.Open(myfilename, FileMode.Create), Encoding.WhateverYouWant))
{    
    sw.WriteLine("my text...");     
}

An alternate way of getting your encoding:

using System.IO;
using System.Text;

using (var sw  = new StreamWriter(File.Open(@"c:\myfile.txt", FileMode.CreateNew), Encoding.GetEncoding("iso-8859-1"))) {
    sw.WriteLine("my text...");             
}

Check out the docs for the StreamWriter constructor.

Simple!

System.IO.File.WriteAllText(path, text, Encoding.GetEncoding(28591));

Wrap your StreamWriter with FileStream, this way:

string fileName = "test.txt";
string textToAdd = "Example text in file";
Encoding encoding = Encoding.GetEncoding("ISO-8859-1"); //Or any other Encoding

using (FileStream fs = new FileStream(fileName, FileMode.CreateNew))
{
    using (StreamWriter writer = new StreamWriter(fs, encoding))
    {
        writer.Write(textToAdd);
    }
}

Look at MSDN