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.
According to Debian's i18n documentation "ja" and "ja_JP" are both valid inputs as I suspected [1]. Qt event accepts it "ja" input.
<pre>
>>> locale = QLocale("ja")
>>> locale.name()
PyQt4.QtCore.QString(u'ja_JP')
>>> locale.language()
59
</pre>

I originally created the Japanese translation file using Qt Linguist and I recall "ja" was the format it gave me. Either way since both works we can use either. I recall @Promm already did the research to confirm which one was the accepted one and went with "ja" based on that, unless I misunderstood our IRC conversation.

[1] https://www.debian.org/doc/manuals/intro-i18n/ch-languages.en.html