本文简单介绍python实现i18n的方法。i18n来源于英文单词internationalization的首末字符i和n，18为中间的字符数，是“国际化”的简称。指让产品（出版物，软件和硬件等）无需做大的改变就能够适应不同的语言和地区的需要，对软件来说，表示在不修改内部代码的情况下，能根据不同语言及地区显示相应的界面，本文以中文和英文作为例子，当系统默认语言是中文时，输出中文，当默认语言是英文时，输出英文。
1）打印英文且支持i18n的python代码i18n_demo.py
#!/usr/bin/env python
# -*- coding: utf-8 -*-
import gettext
import os
appName = 'i18n_demo'
languageDir = os.path.abspath('locale')
gettext.bindtextdomain(appName, languageDir)
gettext.textdomain(appName)
_ = gettext.gettext
print _('This is a translatable string.')
若不需要支持i81n，python代码如下:
#!/usr/bin/env python
# -*- coding: utf-8 -*-
print 'This is a translatable string.'
2）创建pot文件，使用linux下xgettext命令
xgettext -k_ -o i18n_demo.pot --from-code=UTF8 i18n_demo.py
3）生成的i18n_demo.pot文件如下：
# SOME DESCRIPTIVE TITLE.
# Copyright (C) YEAR THE PACKAGE'S COPYRIGHT HOLDER
# This file is distributed under the same license as the PACKAGE package.
# FIRST AUTHOR <EMAIL@ADDRESS>, YEAR.
#
#, fuzzy
msgid ""
msgstr ""
"Project-Id-Version: PACKAGE VERSION\n"
"Report-Msgid-Bugs-To: \n"
"POT-Creation-Date: 2016-03-04 14:29+0800\n"
"PO-Revision-Date: YEAR-MO-DA HO:MI+ZONE\n"
"Last-Translator: FULL NAME <EMAIL@ADDRESS>\n"
"Language-Team: LANGUAGE <LL@li.org>\n"
"Language: \n"
"MIME-Version: 1.0\n"
"Content-Type: text/plain; charset=CHARSET\n"
"Content-Transfer-Encoding: 8bit\n"
#: i18n_demo.py:14
msgid "This is a translatable string."
msgstr ""
4）根据不同语言创建po文件，cn代表中文，en表示英文，使用linux下的msginit命令，中间有停顿，回车即可，依次生成cn.po和en.po文件。
创建中文po文件： msginit -l cn -i i18n_demo.pot
创建英文po文件： msginit -l en -i i18n_demo.pot
5）编辑上一步生成的po文件，切记将charset=CHARSET改成charset=utf-8，将Content-Transfer-Encoding的值改为8bit，然后将对应的中文翻译赋值给msgstr，即只需要编辑3个地方。如下：
5.1）编辑中文cn.po文件
# Language cn translations for py_i package.
# Copyright (C) 2016 THE py_i'S COPYRIGHT HOLDER
# This file is distributed under the same license as the py_i package.
# root <root@leo>, 2016.
#
msgid ""
msgstr ""
"Project-Id-Version: py_i 18n\n"
"Report-Msgid-Bugs-To: \n"
"POT-Creation-Date: 2016-03-04 14:29+0800\n"
"PO-Revision-Date: 2016-03-04 14:38+0800\n"
"Last-Translator: root <root@leo>\n"
"Language-Team: Language cn\n" //zh_CN
"Language: cn\n"
"MIME-Version: 1.0\n"
"Content-Type: text/plain; charset=UTF-8\n"
"Content-Transfer-Encoding: 8bit\n"
#: i18n_demo.py:14
msgid "This is a translatable string."
msgstr "这是一个可译的字符串。"
5.2）编辑英文en.po文件
# English translations for py_i package.
# Copyright (C) 2016 THE py_i'S COPYRIGHT HOLDER
# This file is distributed under the same license as the py_i package.
# root <root@leo>, 2016.
#
msgid ""
msgstr ""
"Project-Id-Version: py_i 18n\n"
"Report-Msgid-Bugs-To: \n"
"POT-Creation-Date: 2016-03-04 14:29+0800\n"
"PO-Revision-Date: 2016-03-04 14:38+0800\n"
"Last-Translator: root <root@leo>\n"
"Language-Team: English\n"
"Language: en\n"
"MIME-Version: 1.0\n"
"Content-Type: text/plain; charset=UTF-8\n"
"Content-Transfer-Encoding: 8bit\n"
"Plural-Forms: nplurals=2; plural=(n != 1);\n"
#: i18n_demo.py:14
msgid "This is a translatable string."
msgstr "This is a translatable string."
6）创建mo二进制文件，使用python的i18n工具msgfmt.py，且需在代码所在目录下提前创建以下目录：
locale/cn/LC_MESSAGES/
locale/en/LC_MESSAGES/
指定中文mo文件输出路径到locale/cn/LC_MESSAGES/，英文的mo文件路径为locale/en/LC_MESSAGES/，mo文件名称必须相同，都是i18n_demo.mo。
创建中文mo文件: python msgfmt.py -o locale/cn/LC_MESSAGES/i18n_demo.mo cn.po
创建英文mo文件: python msgfmt.py -o locale/en/LC_MESSAGES/i18n_demo.mo en.po
7）验证
7.1）设置系统语言环境变量为中文，输出中文：
root@leo:py_i18n# export LANG=cn && python i18n_demo.py
这是一个可译的字符串。
7.2）设置系统语言环境变量为英文，输出英文：
root@leo:py_i18n# export LANG=en && python i18n_demo.py
This is a translatable string.
8）参考
http://underthehood.blog.51cto.com/2531780/1663604
http://www.cnblogs.com/kungfupanda/archive/2012/07/23/2604945.html
