(See the other answers for translate vs. transliterate.)
It's due to Japanese's syllable structure. English allows some spectacularly complicated syllables (strengths being a good maximal example*), but Japanese doesn't - its allowed syllable structure is (C)V(N/Q), where C is any consonant, V is any vowel, N is the nasal ん (which can vary in pronunciation depending on what follows it), and Q is the っ consonant-length-extension-phoneme-thing (which can't occur unless it's before a consonant that can be lengthened).
So you can have words that end in /N/, but most of the time you're going to have a vowel. Primarily this is because almost without exception /N/ only occurs in Chinese loanwords (though a few native Japanese words (especially verb forms) have gained an /N/ since its introduction) - so most native words end in vowels. Indeed, most native words will alternate between consonants and vowels (partly due to Old Japanese not liking adjacent vowels - the most common word shape by -far- is (C)VCV).
There are languages (e.g. most Polynesian ones) which cannot, under any circumstances, have syllables that end in consonants. Japanese used to be that way, but under the influence of Chinese, it has gained two syllable-final consonant phonemes. So you will get words that end in /N/, but mostly words will only end in vowels.
*(English's syllable structure works out to something like (s)(C)(L)V(N/L)(C)(s), where L is either l or r and N is any nasal (n, m, ng) - there are some further rules on which consonants can occur next to each other in certain positions (so trV is okay, but tlV isn't), but that description's mostly accurate. Strengths is pretty much the biggest you can have.)