Ingame language changing

Allow to set|change Language from options menu.
It was not working looong time, lol.

Limitations:
 Change from any specified language("German", "French", "Russian" etc) to "System Language" require CDDA restart.

Tested on Linux and minGW(Codeblocks). Not tested on VisualStudio(but should work).
Undefined reference to set_language.  Same error in main.  Sorry, VlasovVitaly.