There are many foreign languages (mainly from The Europe and The America languages) in Japanese. These languages called foreign words. But in the narrow sense the foreign words are come from the vocabulary of the language of The United States and Europe, most of them are derived from the American English and Anglicism. Foreign words are widely used in the Mandarin of Japan. In daily conversation and articles which use a lot of foreign words, is one of features in Japanese.
1. There are many Chinese words in Japanese. Most of the words are come from Chinese. From the definition of the foreign language, Chinese words should also be part of a foreign language. However, from the point of usage, Chinese vocabulary is not included in the foreign language.
2. Earlier introduction of foreign words, as some of them have been fully integrated into Japanese, almost has no sensation from the foreign language. This type of words is generally written by Hiragana or Kanji in history. Now they are generally written by Hiragana.
3. In the vocabulary which have been already assimilated by Japanese but still have the sensation of foreign languages are generally written in Katakana. The type of words are very stable.
4. The words that have very strong and obvious features of foreign language should be written as the form of Katakana but not Hiragana. The morphology (there means writing) of these words is usually unstable. However a part of them which have ordinary writing form should be written as usual. Such as this kind of the words might use syllables to write but the syllables cannot be found in Japanese language and Chinese language from modern Japanese. These special syllable kana are use to write the foreign words, foreign names and foreign place names, etc. And all of the syllables are closed to original sound or original spelling. These special syllable kana including:
The longues of foreign language
In principle the longues of foreign language use the macron ‘-’to express. For example:オーバーコート（大衣、外套）. But there still have many words are written as vowels instead of the macrons. For explame:ミイラ（木乃伊），バレエ（芭蕾舞），レイアウト（版面设计），ボウリング（保龄球）and so on.
The suffix such as ‘-er、-or、-ar’in principle use macron(-) to write. However they always omitted because of habit. For example:エレベータ（－）（电梯），コンピュータ（ー）（计算机）and so on. And the syllables which behind the part of 「イ」 and「エ」are written as 「ア」. For example：ピアノ（钢琴），イタリア(意大利)and so on. However ,they also written as「ヤ」occasionally. For example：タイヤ（轮胎）,ダイヤル（转盘、刻度盘）,etc.
In the foreign language, there are plenty of words have the different meaning from original words. In Japanese ,the word「アルバイト（あるばいと）」means the students who are still in school doing a part-time. but the original meaning of the「アルバイト」is German while means go to work.
The foreign languages are written as Katakana since they should be very clearly to realize. But in fact there are many words we usually don’t realize that they are foreign words. For example: the word 「タバコ（たばこ）」that original meaning is Portuguese but it usually written as Hiragana 「たばこ」,so many Japanese people think it is originally Japanese language.
On the contrary, although many words written as Hiragana, their original meanings are Japanese language. For example「ナイター(ないたあ) 」，「ワンマンバス(わんまんばす) 」，and they are unknow by foreigner.