Despite the country, sometimes allergies are not taken seriously by healthy people, they just can not imagine that the food they all like is something that could cause harm to other people! so, weird questions and reactions towards this kind of allergy are common. I myself can not eat shrimps and some other sea food, and most people like shrimps so they always ask me "are you sure you don't want to eat it?" or "you will miss a great meal!".
Anyway, Asians are usually respectful when it comes to diet for many reasons one of them is religion. It is totally normal to find some people there who do not eat this or that while others eat this and that, and people respect it, hence I think mentioning that you do not want a certain food to be in your meal will be totally understood without questions or silly reactions. In addition to that, people with allergy are everywhere, so everybody specially restaurant staffs have must faced some people with allergy at some point.
Finally, people with allergy have to make it clear no matter where they are about their allergies. I suggest you learn how to say allergy in the local language and this should make the task easier. Wish you the best.