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.
The return value of the code on Windows is also
```
PyQt4.QtCore.QString(u'ja_JP')
```
So there is nothing wrong with the Windows/Linux thing. It is just my mistake. The only strange thing is how it pass the test.
Should I change the 'tr_ja.ts' to 'tr_ja_JP.ts' under the qtcommon/languages folder or just replace 'ja' by 'ja_JP' in my test tuple?