Character mistake: In her speech outside the bank, Mary Lou Barebone mentions "the wireless" as one of the wonders of modern technology, which is the British term. A New Yorker in 1926 would more likely use the Americanism "radio."
Possibly, but is it probable? Big difference between hearing someone else use it and using it oneself. Just as an example, if I ever were to travel to Britain, it would be an instinctive habit to use words like "elevator" instead of "lift", or "apartment" instead of "flat", simply because to me, as an American, that's what they're called.
Character mistake: Toward the end of the movie, the behavior of Newt is totally out of character - not just for him, but for any sane person. Newt tries to save Credence, and he has just gotten him to stop attacking and actually listening - when the other wizards blast what Newt knows to be essentially a traumatized and abused child to kingdom come. But Newt isn't the least bit distressed or mad, he just shrugs it off in a "shit happens, life goes on" kind of manner, catches Grindelwald for them and helps them save the world, happy as a flea and not giving a damn about the recent death of Credence. Only a complete and utter sociopath would be totally unmoved by the death of a child they were trying to save. A sane, feeling person (like Newt) should be at the president's throat spells blazing, cursing her and the whole American Wizard-hood to the nether regions of hell and not giving a blue damn whether or not they are exposed and in trouble, and whether or not Grindelwald goes free, because in that moment, in his eyes they would be hardly better than him. It is even more out of character since Newt is until that moment depicted as extremely protective of his creatures.
Suggested correction: Newt certainly does show sorrow for not being able to save Credence, but you are putting too much on Newt. Through the whole movie we are shown and told multiple times that Tina is the one close to Credence. She is the one who saved him once before and lost her job for it. Newt is a stranger and tries to help. And also not a powerful enough wizard enough to start fighting the President and her aurors. You decide he shows no emotion which he does, but at the end of the day he is not the one with closest connection to Credence.
Yes, he does show sorrow (which I never claimed he didn't), but only for a moment, and not nearly as much as say he earlier showed when his suitcase, containing mere animals, was taken from him. His reaction neither feels natural nor would be considered normal in a psychological review. Also you completely overlook the fact that newt is close to Tina, and come to think of it, her reaction is hardly normal either considering her history with Newt. Yes, admittedly I drew a rather colorful picture of a possible reaction newt might show, "spells blazing" is probably a bit on the extreme side. He'd probably rather tell her to go to hell and solve her own problems though instead of being eager to help.