IJWTF is right (well, from what I last heard), everyone gets a chance to be at 'the top' of the bidding system, so that month you have a good chance to get what you want. I think then after that the '12' group are the ones who do 'reserve' (if there is such a thing) after the preferences have been filled...
I think you can also swap trips, so long as you are not the preferred language speaker and the person you want to swap with is not. If you are both speakers then it shouldn't be a hassle. Of course swaps would always be subject to operational requirements before personal preference...
