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.
Once you remove the `.qm` extension here like @mtomwing suggests, then it'd better to call this variable `locale`.