OS X Lion now has many different languages available to install in your speech preferences. This is something I've wanted for a long time, because I have long aspired to learn Korean and Japanese. Being able to easily hear things spoken in those languages would really help out.
The problem is that Lion will only speak selected text using the voice that you set as default. I have Alex set as default and when I try to have it speak text using the built-in context menu item, it does nothing.
There is a way around this by using Automator.
First you need to go into the Speech preferences and install any languages that you want to use. Next, open up Automator and make a new Service that receives the selected text in any application. Then add the 'Speak Text' action to the workflow and choose the voice that you want. Finally, save the service with a name that tells you what language it can speak.
Next time you come across some text in that language that you want to hear, select it and right click. The service you made will be in the context menu and you can click it to hear it speak the text you selected.
[crarko adds: You'll need to make a separate Service for each voice you want to use, or write a script that lets you select a voice and use it in the Service instead.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20110722230755650