Docs should recommend uiLanguages

Currently docs recommend using QLocale::system().name() to load QTranslator.

But this wrong. Because there is more powerful method uiLanguages. So, fix your docs, for example, http://qt-project.org/doc/qt-4.8/internationalization.html

This is really important, for example, uiLanguages on GNU/Linux takes info from LC_MESSAGES (and this is right) but name() doesn't take info from LC_MESSAGES (and this is wrong)