Swedish numbers: http://quizlet.com/3614707/speller/
German clothing: http://quizlet.com/1692182/speller/
French animals: http://quizlet.com/1060977/speller/
Japanese adjectives (good luck!): http://quizlet.com/343188/speller/
I also just tried a French one (not the one you linked) and the hints to the side were less than helpful. I guess that's to be expected from a user-generated list. I think I'm also not used to listening to French, and that didn't help... Couldn't really hear what was being said. Again, that could just be my ears, though.
All-in-all, I think it'll be great learning tool... But I thought I'd bring the above to your attention.
1. The photos of the objects could be better, I would suggest designing them against a white background to maintain consistency and type, as some are drawn while others are photographs.
2. I have failed to locate a button to stop the "Keep Going" automatic count down. While its persistence makes me return to it even after switching tabs, some people may find that annoying. I would suggest A/B testing with no automatic countdown and with a "stop" button.
PS: The images of "El pez" and "la catarina" are broken :(
EDIT:
I noticed some audio files sometimes take up to a minute to load (most play instantly though). Chrome/Win7 here.
EDIT2:
It would help if there were an option to play both Italian and English audio, just to use the auditory memory.
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?
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 :)