Fix #476 Auto language changing function finished.

Fixes issue#476.
If the user does not have the freeseer.conf file, the function will detect the system location for default language.
If there is a config file, the language setting in that file will have higher priority.
For Chinese, If the location is not zh_CN, Traditional Chinese will be used.
If there is no translation for the system location, English will be used.
It looks like "ja" is a shorthand that Qt allows. Other locales also have shorthands. E.g.
```python
>>> QLocale("en").name()
PyQt4.QtCore.QString(u'en_US')
>>> QLocale("ar").name()
PyQt4.QtCore.QString(u'ar_SA')
```

But I don't think it's standard, as all the resources I come across indicate that language_country is standard. 

Note that the Debian documentation you linked to doesn't recommend using "ja".

> LANG=ja (because EUC-JP is the de-facto standard for UNIX; not recommended)

So I vote for using the language_country variant since that seems to be the norm.