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?