Bug#576653: Language selection should use current locale

[Werner Mayer]

Hi Jens,

this is something we have already implemented in our current developer 
version (0.10).

Instead of using the suggested environment variables or function we use 
the Qt API therefore. It provides the class QLocale which allows us to 
get the language name with 
"QLocale::languageToString(QLocale::system().language())".

Now, the system language is determined at startup but can be still 
overridden by the user if he has selected another default language than 
the system language.

BTW, when starting FreeCAD we set the variables "LANG" and "LC_ALL" to 
"C" because otherwise we run into problems when loading or saving CAD 
files. This was addressed in item #559846.

Regards,
Werner