If you have some multimedia-dictionaries installed, they may contain sound files that let you hear pronunciation of some words. If a dictionary contains a sound file corresponding to a certain entry, you will see a standard QuickTime progress bar right above that word's definition/translation. Click the play button to hear its pronunciation.
And even if you don't have any dictionaries with sound files, TranslateIt! still allows you to hear any word's pronunciation using Mac OS X built-in Text to speech feature. (However, it is not recommended to learn foreign words' pronunciation using it.)
Translating with TranslateIt!
Accessing TranslateIt! features globally
Let TranslateIt! suggest
Managing notes