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.
Removing the last three characters is risky. According to http://qt-project.org/doc/qt-4.8/qlocale.html#name

> country is an uppercase, two- or three-letter ISO 3166 country code

So it's safer to split on '_' if you just want to grab the language.