This word is taken from French. That is why it may look un-English. It also accounts for the fact that it sounds un-English - although there are several pronunciations
In educated English RP, the tradition is to sound as like French as possible - the final '-s-' is silent, and the two syllables are equally stressed IPA: /ˈfræ kɑː/. In American speech, it is pronounced much more as it looks - with the stress on the first syllable, which rhymes with 'take', and the second syllable quite like 'us' IPA: /ˈfreɪ kəs/.