[kd1221]

Did you check out Festival/Festvox/Cepstral? http://festvox.org/ Festival/Festvox are free to use. I built an Arabic speech synthesizer with it in the spring of 2002 for a class project. It's quite flexible. Cepstral is a commercial offshoot of Festvox.

I ran through a few of the foreign language quizzes (German, Spanish, Arabic) and they're pretty good. They do need a bit of curation, because some of the answers required superfluous punctuation (Food = "das Essen -"). Some data scrubbing is in order.

The quizzes with non-Latin alphabets are a bit difficult to do, but understandably so. The beauty of these languages is in their writing anyway. Are you planning any iPad/tablet apps?

[asuth]

We decided the most realistic audio came from commercial vendors.

In terms of mobile stuff, we've thought about doing our own but for now there are great apps being built on our API. We just launched V2 of our API with OAuth integration: http://quizlet.com/blog/quizlet-announces-api-2/

If anyone's interested in building mobile stuff, feel free to play around with it. Or contact us (email in profile) and we may have a job for you :)