Again the pidgin syndrome has kicked in.
How astounding to see you open with an off-topic ad hom attempt at an insult. But I suppose you can't argue with the facts, so all you have left are personal comments.
In this context aplikacja is not an English application, ...
I'm well aware of what an aplikacja adwokacka is, but you clearly are not. It's not an internship. Interns are unqualified unpaid students. An aplikacja adwokacka has already graduated from law school and is completing his training to be accepted by the Bar Association. They are training to be admitted to practice for their chosen speciality. In the case of the leader of Poland's resentful and frustrated poor losers' camp, Chairman Kaczynski, he chose to become a prosecutor.
Prosecutors even in totalitarian countries like PRL did not deal solely with poltical dissdients
Of course they didn't. But they also prosecuted political 'crimes', prosecuted dissidents. It's not as if there was a box on the application form to tick marked 'Will not prosecuted dissidents'. Chairman Kaczynski signed up to prosecute both real criminals and those whose only crime was to want Poles to be free.
the twins were raised in a very patritoic pro-AK, anti-communist atmosphere
Yes, because the commie regime were noted for giving villas worth millions and the best jobs and education to very patritoic pro-AK people, weren't they? And former AK officers who turned traitor were punished by being given the worst jobs and accommodation, weren't they.
Why woudl Jarek sudde turn on his mum and favour a repressive system he had learnt to despise?
Clearly he didn't despise it, as he signed up to prosecute those to tried to end it.
I don't like 'trainee advocates' and would probably say something like 'legal traineeships'
No, because these aplikants are strictly delineated between the speciality they will follow (aplikacja radcowska, aplikacja notarialna, etc). In the case of Chairman Kaczynski he chose to be an aplikant prokuratury and thus to become a prosecutor, at a time when that meant prosecuting dissidents.