Now google has stop providing free translation API. So I have to switch to http://mymemory.translated.net/, which has a limit for 1000 words/day free usage. Please let me know if there's any other better free translation API.
The default from language is English (en). The default to language is Simplified Chinese (zh). Of course, you can specify it in the parameter or commandline.
利用google translate实现的命令行工具（translate），也可以当做Python模块用在你的代码中。
pip install translate
Or, you can download the source and
python setup.py install
Add sudo in the beginning if you met problem.
In your command-line:
translate "This is a pen."
Or
translate -f zh -t ja 我是谁？
from translate import Translator
translator= Translator(to_lang="zh")
translation = translator.translate("This is a pen.")
The result is in translation, and it’s usually a unicode string.
Free, anonymous usage is limited to 1000 words/day. To get more words/day add your email-adress in the Translator-class. For further usage contact mymemory as CAT tool maker: http://mymemory.translated.net/doc/usagelimits.php
In ~/.python-translate.cfg:
[DEFAULT] from_lang = auto to_lang = 'de'
The cfg is not for using as a Python module. The country code, as far as I know, is following https://en.wikipedia.org/wiki/ISO_639-1.
Please send pull requests, very much appriciated.
If you find an incorrect translation, one thing you can do is to create an account at http://mymemory.translated.net/ and fix their data.