It's late and I'm tired, so my reply may be really stupid but here goes: if we're both looking to turn left, who decides who's going to be first and last? I thought that the different trajectories method you suggested earlier seemed the best suggestion, ie we both can go via separate trajectories. If I go first or he goes first, we'll pass each other on our right even if neither of us intends to go straight, so what factor then decides who goes first? My head hurts... sorry but I can't work this out, I hope it's because it's late and not my IQ dropping permanently.
2. If you are going to turn left and opposite car is going to turn (his) right, you should give him a way (and save his driver-side door ;)
That's easy to understand. Usually they just turn right without waiting anyway, so there's no possibility of going before a car turning right.
I'm going to see if I can find the English version of the Polish Highway Code, with diagrams, because at the moment I feel very insecure when driving here and that ain't good for anyone.
Again, I should reiterate, if the junction/crossroads allows it, both cars turning left should probably drive cautiously forward and then pass behind each other because that's what we do in the UK officially and it works fine when both drivers stick to it and recognise the other one's MO. Problem is not all junction layouts allow that system. Best thing they could do at this particular dodgy crossroads is put in a mini-roundabout, btw. In the UK, some towns have mini-roundabouts every few streets. It can be annoying to have them everywhere but I prefer them to traffic lights (which are much more expensive anyway).