C#

public enum Pitch : byte
{
    Default = 0x00,
    Fixed = 0x01,
    Variable = 0x02
}

public enum Family : byte
{
    DontCare = 0x00,
    Roman = 0x10,
    Swiss = 0x20,
    Modern = 0x30,
    Script = 0x40,
    Decorative = 0x50
}

using System;
using System.Runtime.InteropServices;

class EnumFonts
{
  static void Main(string[] args)
  {
    string family = null;
    if (args.Length > 0) family = args[0];

    // Get the HDC for the desktop.
    IntPtr hdc = GetDC(IntPtr.Zero);

    try
    {
      EnumFontFamilies(hdc, family,
        new EnumFontFamProc(Callback), IntPtr.Zero);
    }
    catch (Exception ex)
    {
      Console.Error.WriteLine("There was an error enumerating the " +
        "font families: " + ex.Message);
    }
    finally
    {
      ReleaseDC(IntPtr.Zero, hdc);
    }
  }

  static IntPtr Callback(ref ENUMLOGFONT font, ref NEWTEXTMETRIC metric,
    int fontType, IntPtr lParam)
  {
    Console.WriteLine(font.FullName);
    return new IntPtr(1); // Continue enumeration.
  }

  [DllImport("user32.dll")]
  static extern IntPtr GetDC(IntPtr hWnd);

  [DllImport("user32.dll")]
  static extern IntPtr ReleaseDC(IntPtr hWnd, IntPtr hDC);

  [DllImport("gdi32.dll", CharSet=CharSet.Auto)]
  static extern IntPtr EnumFontFamilies(
    IntPtr hdc,
    string family,
    EnumFontFamProc proc,
    IntPtr lParam);

  delegate IntPtr EnumFontFamProc(
    ref ENUMLOGFONT font,
    ref NEWTEXTMETRIC metric,
    [MarshalAs(UnmanagedType.U4)] int fontType,
    IntPtr lParam);

  [StructLayout(LayoutKind.Sequential, CharSet=CharSet.Auto)]
  struct LOGFONT
  {
    public int Height;
    public int Width;
    public int Escapement;
    public int Orientation;
    public int Weight;
    public byte Italic;
    public byte Underline;
    public byte StrikeOut;
    public byte CharSet;
    public byte OutPrecision;
    public byte ClipPrecision;
    public byte Quality;
    public byte PitchAndFamily;
    [MarshalAs(UnmanagedType.ByValTStr, SizeConst=32)]
      public string FaceName;
  }

  [StructLayout(LayoutKind.Sequential, CharSet=CharSet.Auto)]
  struct ENUMLOGFONT
  {
    public LOGFONT LogFont;
    [MarshalAs(UnmanagedType.ByValTStr, SizeConst=64)]
      public string FullName;
    [MarshalAs(UnmanagedType.ByValTStr, SizeConst=32)]
      public string Style;
  }

  [StructLayout(LayoutKind.Sequential, CharSet=CharSet.Auto)]
  struct NEWTEXTMETRIC // Also TEXTMETRIC for non-TrueType fonts
  {
    public int Height;
    public int Ascent;
    public int Descent;
    public int InternalLeading;
    public int ExternalLeading;
    public int AveCharWidth;
    public int MaxCharWidth;
    public int Weight;
    public int Overhang;
    public int DigitizedAspectX;
    public int DigitizedAspectY;
    public char FirstChar;
    public char Lastchar;
    public char DefaultChar;
    public char BreakChar;
    public byte Italic;
    public byte Underlined;
    public byte StruckOut;
    public byte PitchAndFamily;
    public byte CharSet; // TEXTMETRIC ends here
    [MarshalAs(UnmanagedType.U4)] public int Flags;
    [MarshalAs(UnmanagedType.SysUInt)] public IntPtr SizeEM;
    [MarshalAs(UnmanagedType.SysUInt)] public IntPtr CellHeight;
    [MarshalAs(UnmanagedType.SysUInt)] public IntPtr AvgWidth;
  }
}

Must be set to zero for all language versions of the operating system.