Firstly, you must know how the word is spoken in the native tongue. Then you must understand the limits of Japanese vowel sounds. You then find find the closest match. Those are the rules. Arbeit = アルバイト Paris =　パリ computer = コンピューター

It's kind of hard to make a set of rules concerning English <> Katakana transcription. Obviously, the katakana is based only on the English word's pronunciation, and altered to fit the Japanese palate. Ls become Rs, Vs become Bs, words ending in "er" are changed to "aa". Even after that there are occasionally some differences, though. When in doubt, deshijisho.org

All words loaned form ANY language are written in katakana. I don't quite understand your question about "translating" words in katakana.

Please tell which English vocabularies appears in the form of katakana in Japanese?