To have a career in translation or interpreting, would I have to study a specific field such as politics, econ?

In September 2012 I am due to go to university and I am thinking of doing a combined degree of Spanish (which I know a lot of) and Arabic (which I have a basic knowledge of) HOWEVER when researching careers in languages i.e. interpreting and translation, it seems that you need an in-depth knowledge of the field you are going to be working in, so for example if I wanted to work for the UN then I would have to have studied politics. This would mean I could only study ONE language if I have to study a subject like politics too but I want to do both languages. Anyone who has any knowledge of what is required or can help is appreciated. Thanks X