Depending on what you consider an "English" word, anywhere from 0% to 100% of words are English words. I've definitely seen accoutrement and ziggurat in English, and quite often.
Of course, the line is very blurry. I've used accoutrement(s) in English many times, but I've never considered myself to be speaking English when I use it. It's like joie de vivre or c'est la vie.
Of course, the line is very blurry. I've used accoutrement(s) in English many times, but I've never considered myself to be speaking English when I use it. It's like joie de vivre or c'est la vie.