OS X includes excellent text-to-speech capabilities, activated in System Preferences/Speech/Text-To-Speech or doing Command + F5 to turn on VoiceOver (System Preferences/Universal Access/Seeing/VoiceOver). Unfortunately the supplied voices only do English. Users who need other languages need to acquire third-party voices and sometimes use non-Apple applications.
Speechissimo and Cepstral offer French, German, Italian, and Spanish.
AssistiveWare has several different products. TextParrot offers French, German, Italian, Danish, Dutch, Finnish, Flemish, Spanish, Portuguese, Norwegian, and Swedish. For more features, there are Infovox iVox, VisoVoice, and Proloquo.
The application Key5 has a Chinese text-to-speech module.
DTalker is said to be able to do Japanese text-to-speech.
OS X 10.5 Leopard, to be released the spring of 2007, is expected to include expanded support for foreign language add-on speech synthesizers, including Chinese and Japanese.