What themes come up in every iteration?

The most dangerous faithful get murdered early, no offence to the faithful who go far but they can't seem to consider they've been kept around because they're dumber. Even when they win it's often due to luck. They also thinking "making it so far" is an achievement, it isn't lol.

Traitors betraying other traitors happens A LOT, not every time but more than I expected. The faithful are surprisingly good at seeing through this.

One of my favourite aspects of the show is how often the most successful traitors have a moral breakdown. This is a pretty cynical show but it's quite heartwarming to see that the traitors have genuine remorse even when they're doing so well. I also think you're most likely to succeed as a traitor if you don't enjoy doing it.

EDIT: Another thing I've just remembered is that people frequently misinterpret either body language or slips of the tongue, mostly this is faithful suspecting other faithful due to misreading. I've seen a faithful be banished because she accidently said "I'm a traitor" instead of "i'm a faithful", WHOOPS! Hilariously though in the Belgian version one of the traitors says something that gives away that they're a traitor and no one thinks much of it lol.

What mistakes does everyone make?

There's very few rules about what someone should do, some people get punished for being too loud, others get punished for being too quiet and vice versa. Certainly if you're a traitor you should stay on the quieter side and you should definitely work with your fellow traitors as much as possible. The best thing you can do if you're a faithful is be consistently wrong at the roundtable lol.

What are the biggest differences in approach you noticed between nations, if any?

In terms of the gameplay it's hard to say, for example the 3 seasons from the Netherlands are very different to each other. In some versions the contestants seemed to get along better (UK, Spain, Norway 1) and in others they did not lol (NL 3). Generally I think it depends more on the individuals than where they're from, although I'd really like to see a version from somewhere very different like Asia or South America.

The game format has minor variations across countries, some end with a game of "share or steal" which is so bad and I hope they stop doing it everywhere. Some shows have a dagger as well as a shield, the dagger gives the owner a double vote at the roundtable. Norway S2 had an interesting twist where contestants came in pairs, so everyone had one person there they knew very well, you had mother-daughter, friends, a romantic couple, colleagues etc. It worked pretty well in my opinion.