Is it even possible to slow it down? I feel that it speaks extra fast in French.
There's no way to control talking speed in the Translate site (and you're right, it does speak pretty fast in French), nor is there any provision for it in the Google Translate API.
(For the record, this is true for 10/11/11, so please, don't deduct points from this 2 years from now if/when Google starts providing speech controls :))
If Google Translate deems your browser to be capable of playing audio via HTML5 sufficiently, it will use it. Otherwise, it will use Flash to play the audio.
You can execute this via your browser's console or create a bookmarklet by prepending the code with
Note that I have only tested this in Chrome, so I am unsure whether it'll work in other browsers. Also, the slowest and fastest rates at which my browser still plays the audio are 0.5 and 4.0 respectively.
One CAN slow Google Translate down by inserting spaces and full stops;
eg " Your . . . French . . . . class . . . . was . . . . wonderful. . . . . . "
will slow the speech down somewhat.