An enemy plane was shot down after it violated the exclusion zone.

“禁区”本身就是规定不许进入。An exclusion zone is an area where people are not allowed to go or where they are not allowed to do a particular thing, for example because it would be dangerous.

violate 意为“违犯，违反，违背，侵犯；扰乱，妨害，妨碍；冒犯，亵渎，玷污”。

所以，“规定”二字属于多加的“意译”。

翻译成：“飞机侵犯了、冒犯了禁区”也完全可以，这样就不用“规定”二字了。这属于翻译变通，无须忧虑。