fix handling of country-less languages like esperanto

fix handling of country-less languages like esperanto

it's impossible to instantiate QLocale objects like that, so the
language setting would be simply clobbered. instead, we now convert
between numerical and string codes directly.

unfortunately QLocale has no public api for that. but we are including
private QTranslator headers already anyway, so whatever.

Task-number: QTBUG-14592
Change-Id: I95189c1898aa1fb5520ecf7057521597ed9331f1
Reviewed-by: hjk <hjk121@nokiamail.com>
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>