This is extremely helpful to carry around so that the person serving you food, or offering you any service is aware of your allergies or restrictions. The translation isn’t a simple Google Translation, but rather in terms the person from that country will understand. Also, no one wants to purposefully make your dining unpleasant, and this will take away the potential for much back and forth confusion. Keep in mind that you are their guest too.

I have food allergies...
I have food allergies...