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.
Not a big deal, but I would personally try to avoid the negative case, e.g.

```python
if os.path.isfile(language_path):
    return locale + '.qm'

return 'tr_en_US.qm'
```

This works better with the `locale` variable name, because `locale = "tr_en_US.qm"` isn't very accurate since you're assigning a filename, not a locale.