Ya

Just a direct translation

I call the Facultat de Ciències at the Universitat Autònoma de Barcelona (for which I translate the website) the "Faculty of Science". This is what it would be called in the English-speaking world. Of course, it depends on what courses are given in that faculty at your university, but at the UAB, this faculty is for the "Pure Sciences". I find "Science" more precise, since there are other faculties that teach other sciences (indeed, in the Catalan and Spanish, many of the other faculties have "Ciències/Ciencias" in their name. By using the singular in English, it is clearer that it is referring to the pure sciences.

As for Faculty/College, in the US it would be college and in the UK and elsewhere it would be Faculty. I would use Faculty anyway so that it is clear that in the particular country this is what they are called. For the same reason I wouldn't call the "Rector" the Vice-Chancellor (UK) or Chancellor (US).

At least in Canada, (and I know in the US as well), at the University level, Humanidades is the equivalent to Arts. Two US examples below.
Good luck and I hope it helps.

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Note added at 6 hrs 1 min (2005-12-19 02:12:13 GMT)
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Here's an example from Canada
http://www.artsandscience.utoronto.ca