之前在很多地方都能见到I18N，特别是open source里面。I18N就是Internationalization的缩写，其原因是I和n之间一共有18个字母。

下面这些地方会需要I18N

• Displaying characters for the users' native languages.
• Inputing characters for the users' native languages.
• Handling files written in popular encodings that are used for the users' native languages.
• Using characters from the users' native languages for file names and other items.
• Printing out characters from the users' native languages.
• Displaying messages by the program in the users' native languages.
• Formatting input and output of numbers, dates, money, etc., in a way that obeys customs of the users' native cultures.
• Classifying and sorting characters, in a way that obey customs of the users' native cultures.
• Using typesetting and hyphenation rules appropriate for the users' native languages.

当然除了I18N还有L10N(localization) 和M17N (multilingualization)，这3个之间有什么区别呢，举例说明。

L10N支持2种语言，英文和另外一种语言（例如中文）；

I18N支持多种语言，但是同一时间只能是英文和一种选定的语言，例如英文+中文、英文+德文、英文+韩文等等；

M17N可以在同一时间支持多种语言，例如你可以在一个页面里看到中文、英文、德文和韩文。