In contemporary Japanese writing, foreign-language loanwords and foreign names are normally written in the katakana script, which is one component of the Japanese writing system. As far as possible, sounds in the source language are matched to the nearest sounds in the Japanese language, and the result is transcribed using standard katakana characters, each of which represents one syllable (strictly mora). For example, America is written アメリカ (A-me-ri-ka). To accommodate various foreign-language sounds not present in Japanese, a system of extended katakana has also developed to augment standard katakana.
Katakana, like hiragana, has a one-to-one correspondence between sounds and characters. Therefore, once the "Japanese sound" of a word is established, there is no ambiguity in its katakana spelling (unlike spelling in English, for example).
A much less common form of transcription, Ateji, uses kanji characters for their phonetic values.
Practicalities of transcription
Word length
Because Japanese is written with relatively complex Kanji characters, Japanese text must generally be written larger for legibility. Furthermore, as both Kanji and Kana are traditionally of equal width and height, Japanese characters are generally much larger than Latin characters. As Kanji are logographic and Kana encode entire syllables (or rather, morae), the higher information density of Japanese writing usually evens out with the larger text so that Japanese and English texts take about the same amount of space, but challenges arise with foreign consonant clusters incompatible with Japanese phonotactics and the Kana system. For example, the word remote control becomes the cumbersome リモートコントロール (ri-mō-to-ko-n-to-rō-ru) in Japanese. Here, additional vowels are added between and , between and , and after at the word's end, and the vowels of mo and ro have been lengthened to mimic the English pronunciation. These additional sounds not only add to the word's length when spoken, but it also severely bloats the word when written. As such, the word is typically shortened to simply リモコン (ri-mo-ko-n) in modern Japanese speech and writing.
Syllable structure
Since Japanese has few closed syllables, syllable-final consonants in the source language are often represented using the -u (or sometimes -o or -i) kanas with implicitly silent vowels – though this vowel often is pronounced in Japanese – or the syllable coda is not represented at all. For example, the name Jim is written ジム (Ji-mu). A similar principle applies to consonant clusters; for example spring would be transcribed as スプリング (su-pu-ri-n-gu), and scratch would be transcribed as スクラッチ (su-ku-ra-cchi).
Diphthongs
Japanese has only five native vowel sounds, each a pure vowel (monophthong) with a long and short form, and some degree of approximation is necessary when representing vowels from, for example, English. Diphthongs are represented by sequences of vowels, and pronounced with hiatus, as a sequence of discrete monophthongs, not a diphthong, as in ブラウン Bu-ra-u-n "Brown", ナイス na-i-su "nice", ディア di-a "dear/deer", レア re-a "rare". etc. The English spelling <ore> (phonologically /ɔː/ (RP) or /ɔːr/ (GA)) is usually "diphthongized" as o-a in Japanese (e.g. コア ko-a "core"), possibly because it is also pronounced as a diphthong (/oə/) in some accents of English. The English /eɪ/ is transcribed to either e-e (エース e-e-su "ace") or e-i (スペイン Su-pe-i-n "Spain"); similarly, /əʊ/ is transcribed to either o-o (ショー sho-o "show") or o-u (シャドウ sha-do-u "shadow").
Phonemes
Japanese does not have separate l and r sounds, and l- is normally transcribed using the kana that are perceived as representing r-. For example, London becomes ロンドン (Ro-n-do-n). Other sounds not present in Japanese may be converted to the nearest Japanese equivalent; for example, the name Smith is written スミス (Su-mi-su). Foreign sounds can be difficult to express in Japanese, resulting in spellings such as フルシチョフ Furushichofu (Khrushchev), アリー・ハーメネイー Arī Hāmeneī (Ali Khamenei) and イツハク・パールマン Itsuhaku Pāruman or イツァーク・パールマン Itsāku Pāruman (Itzhak Perlman).
The English voiceless labialized velar approximant /hw/ (orthographically wh), which is a distinct phoneme from /w/ in some varieties of English, can be transcribed as ho(w)-. For example, White is ホワイト Howaito, whale is ホエール hoēru.
French /w/ is typically transcribed as u, but the sequence /wa/ is as o-(w)a (e.g. ポアロ Po-a-ro "Poirot").