If the word have an equivalent in Arabic it is simply translated, but when the word is unique and refer to things or meaning that is not known or used in Arabic culture; so it is transliterated with Arabic alphabet. Ravioli = Rafioli, because there i not a /v/ sound in Arabic.

It depends on the word. If this word is something known here, you may find a translation for it. If it's something that we don't know then of course we don't have translation for it and we use the foreign word. Also, it depends on which Arabic you're speaking, for example in Egyptian dialect we use many foreign words, even if there's a translation for this word. In standard Arabic, we try to avoid foreign words and use the Arabic translation as much as possible.

As far as I can tell, both of your examples are transliterated when written in Arabic. Here's how you can find out: 1) Use Google Translate, then copy the result into a general search. An image search also helps (when I did this, the search also corrected the word that Google Translate had given me). 2) Look up the word on Wikipedia. Go to the languages on the left-hand side and switch to a different language (if the language you want is available). Still, the most important thing is to check with a native speaker, but try doing the groundwork first. :)