This is quite easy, for those languages where text-to-speech is supported by available Microsoft
language packs for Windows. I personally know only the support for English, not sure about other languages (I suspect this is only English, not sure; for other languages, third-party products may exist; I just heard of some of such things).
All you need is to reference the assembly "System.Speech.dll". This assembly is actually bundled with .NET Framework, placed in the GAC, so you will need to reference it via the tab ".NET" of the "Add Reference" window, in case you use Visual Studio.
Please see
System.Speech.Synthesis
part of the .NET Speech API:
http://msdn.microsoft.com/en-us/library/system.speech.synthesis.aspx[
^].
Using it is really simple, the documentation referenced above is complete with clear code samples.
—SA