"English" seems a sensible term in that context. They don't want to use "Imperial" because they're American (and if they gave measurements of volume or weight, "Imperial" would be incorrect anyway), and they don't want to use "US customary measures" because they're aware that they have an international audience. But the three countries which don't officially use metric measures all speak English to some degree, and the vast majority of people choosing to see miles and fahrenheit will be English speakers.