Kinkytoes and kelly, thanks for your support, it's good to know others would find this behaviour unacceptable as well. Kinkytoes, I agree completely that a little consideration for neighbours goes a long way. It's very thoughtful to let them know when you're sleep-training, and having this knowledge I'm sure they will be extra understanding.
Mamadoc... your post contains many inaccuracies. I have never referred to this family as 'poor illiterate immigrants' (your words). I have pointed out there is a language barrier, which makes direct communication difficult, and that they may be less aware of local services and at greater risk of isolation because of this. All relevant to the topic.
Since this is a thread on a pregnancy forum, on a parenting website, I think everyone (even mums-to-be) has a right to share, discuss and debate parenting strategies, and express opinions, without being called 'smug' or being ridiculed.
It is as much about ethical issues as specific parenting strategies.
And even if a mum-to-be shares something she has read in a book, or heard from a friend, she is still entitled to raise it and find out what others think/if others have tried it.
I stand by my belief that parents living in flats need to be respectful of neighbours and minimise the noise their children make at night. To most people this is common sense!
Yet it appears some lose sight of the bigger picture when they have a child, forgetting that courtesy, respect, consideration and good manners are still necessary when you live in close proximity to others.
It's eye-opening just how many people think it's ok to let toddlers make as much noise as they want all night, run around banging on partition walls etc! They expect endless patience and understanding from neighbours 'for a few years' yet couldn't care less that their child is repeatedly waking these people night after night!
Amantes... there is a cut-off point to ignoring excessive relentless noise from neighbours, child or no child. While it's easier for parent to label neighbour as having 'sensitive hearing coupled with busybody nature' this is shelving responsibility and failing to attend to the problem at hand. Why not blame the neighbour for being unable to sleep through your child's excessive noise? What a great solution! That way you don't have to bother to take any action at all! 
When your child's noise is loud enough to wake people in next flat (despite earplugs) your neighbour is hardly 'oversensitive'! As for 24-hour screaming, crying and hitting walls... is that your idea of a 'happy family home'? ROFL
Luxurytrifle, would you let your child hammer on partition walls at night and run around screaming until 3am? Is this an example of 'gentle-parenting'?! You seem to think it's cruel to keep a child in his bedroom at night by using a stairgate. The obvious answer, if parents feel he should be allowed run of the house all night, would be to stay up with him and keep him entertained. I'm sure plenty of responsible parents do stay up at night with toddlers and keep them from waking neighbours.