After searching a proper webquest for foreign language learning, I found it is pretty limited to Grade 9-12 and adults, and to French and Spanish. There are some Chinese webquest, but the links are not complete and the levels are usually too high for K-5. Here is one model, which might be a good example for building up K-5 foreign language webquest, though it is not designed for specific language.: http://zunal.com/process.php?user=30447
One thing language teachers can do is that adapted the processes and materials from the webquest to your language class and your students' level.