Downloading International Voices for Mac OS X
Mac OS X 10.7 Lion allows downloading high quality voices to speak 27 international languages and some dialects: Arabic, Czech, Danish, Dutch, Finnish, French, German, Hungarian, Italian, Japanese, Korean, Norwegian, Polish, Portuguese, Russian, Spanish, Swedish, Turkish, Cantonese, Mandarin, Greek, Hindi, Indonesian, Romanian, Slovak, Thai. You can download these from within the Systems Preferences. Choose Customize from the Voice pop-up menu in the Speech pane.

• Read4me has been localized in six languages, see the screenshots in:
Dutch, English, French, German, Italian, Spanish.
This means the program’s menu’s, dialogs, etc. have been translated so that it has a native feel for those languages.

• Mac OS X 10.6 Snow Leopard provides English text-to-speech, with a very high quality voice Alex. Alex uses advanced Apple technologies to deliver natural intonation in English even at extraordinarily fast speaking rates. Speech in other languages it possible (see below) You don’t need Mac OS X Lion to use text-to-speech in international languages, you can download additional voices from other vendors. And they have free demo’s available.

Listed below are third party products, and the links below are provided for your convenience only. Read4Me is independent of speech engine, some engines deliver more features than others.

Cepstral
http://cepstral.com/downloads/
Download
free demos, trial period is not time-limited, but reminders appear in the audio output.
Single User License $29.99 per voice (Credit Card/PayPal)
Italian, Canadian French, German, Americas Spanish, UK English, US English, Special Characters

CereProc
http://www.cereproc.com/en/products/Mac_OSX_voices
Online samples
Irish English, Scottish English, Southern English, West Midlands, US English, Austrian German, German
€34.99 per voice (Credit Card/PayPal)

Infovox iVox
http://www.assistiveware.com/voicedownload.php
free demos (30 days) high quality voices in these languages:
Arabic, Czech, Danish, Dutch, Finnish, French, German, Greek, Italian,
Norwegian, Polish, Portuguese, Russian, Spanish, Swedish, Turkish
Licensing is more expensive, but they include male and female voices, and they are of a higher quality than Cepstral’s.
First Single User License €99, additional languages €99.00 (Non-Scandinavian), €219 (Scandinavian), (Kagi store)