Today I found this wonderful English language Japan blog called Surviving in Japan. Now that I have extensive food allergies, I've often wondered how I would eat if I were to visit Japan. Surviving in Japan has a really detailed guide to reading food labels for allergy information. There's also a fantastic general guide to reading food labels. While foreign food sold in the United States has to have English labels, once in a while I come across an item at the store that doesn't have an English label. I'm not sure I'll want to print the guide and carry it out for those rare times when I might need it, but it's nice to know it's available if I change my mind or if I ever go to Japan again.
Other Japanese allergy resources, which might even be helpful in the US if you want to go to Japanese restaurants with waitstaff who don't speak much English: