Mweb 853 querystring

@nandy-andy @RafLeszczynski @rogatty I checked and all our units tests are passing, jenkins unit tests failure might be caused by sth else (?) 

BTW. Sorry for no unit tests for this, i will surely add them on Monday.
`F::app()` is not needed here -- it's a public method in our `WikiaController` so we can use magic :fireworks: and go with `$this->wg->Lang->getCode()` instead.