Yaya Lu (the teen who has been featured on here before) has another project up.
In this project, she uses the sound sensor and some RobotC software to tell the difference between a 'dit' and a 'dah' (effectively Morse Code). That then sends a signal via a NXTBee sensor to her wheelchair (teddy bear included of course) to make it move around.
As she points out, there are over 7000 languages, so rather than an expensive solution to learn all of them, simple long and short sounds are a better way to go.
Check out her video, it does a great job of explaining how she went about solving the problem.
More info here - http://www.yayalu.net/Yaya-Lu-2012/Yaya-Lu-2012.htm