Last year I uploaded a series of printable cards for communicating dietary restrictions in Japan . This is a follow-up of sorts to this, with some information about food package labelling and allergy-causing products.
There are 7 substances that must, by law, be indicated as being present on packaged foods that contain them in Japan. I’ve listed them below in this order: English: kanji: hiragana or katakana: roma-ji.
Then there are 18 other food substances that are recommended to be indicated if they’re present.
About oranges - I do wonder if it includes satsuma and clementines and mandarins and such, which are called oranges in the west but are called 蜜柑 - mikan - in Japan. I guess logically it should. Anyway, if you are allergic to oranges including the ‘mikan’ kind watch out for the オレンジ label.
Here are two examples of allergy-food labels. This one just shows the 7 must-show substances, with a black dot under the ones that are in the food. (Remember that Japanese can be written horizontally left to right or vertically.)
The one below shows all 25 substances in a grid, with the ones that are in the product indicated in black. I think this one makes more sense and would like to see it standardized.
The point is to always look for the words that indicate whatever you are allergic to, even if your personal Kryptonite is not included in the substances listed above. And when in doubt, pull out one of your allergy-communicator cards and ask someone. Just pointing to a package, then showing your card, and saying, “OK?” with a helpless look on your face will be enough, I promise. Many people in Japan are quite happy with helping hapless visitors.
If you can read Japanese, there’s an informative PDF on the Japanese government’s Consumer Affairs Agency (消費者庁) site about allergy-causing food labeling: link to PDF .
See also: my related Quora answer here  for a couple more labels.
The cute samurai warrior cat(?) character up top is the mascot of a non-profit food safety consumer hotline  (Japanese only I’m afraid). Of course they have a cute mascot - it’s Japan, what do you expect? ^_^