Ling, Lan Fan, Fu, and Mei speak in extremely proper and formal Amestrian. Particularly Ling and Mei, because they were taught Amestrian (and several other languages) for diplomatic purposes. Prior to travelling to the country, their experience with the language had been limited to pretty much teachers and textbooks.
With Mei it kinda fits. I mean, it is kind of strange that she addresses kids just a couple of years older than her as "Mr." but her demeanor overall (even when she's angry or fighting and demonstrating how fierce she is) is so polite that it's not that incongruous.
Fu is old and has this air about him, like he's nobility but not, so that checks out. And you can see Lan Fan's stickler attitude to protocol for miles.
Ling talks like he's writing a business email and it's so fucking weird. It clashes with the everything about him so badly. He eventually adapts and his speech turns far more informal (particularly after he shares a brain with Greed for months), but when he meets the Elrics in Rush Valley he's only been in Amestris for a couple of weeks and is still going off what he'd been taught by his Amestrian tutor. It's actually the first thing that clues them in the fact that this guy's probably rich, even before Fu and Lan Fan appear and address him as "my lord," because no one without money would use fucking "whom" in a casual context.
Those early days, sometimes he does throw in the rare slang expression, except it's something he'd picked up from a literary classic that he'd had to read and it's several decades (or centuries) outdated, so Ed just. Stares at him. Wondering why the fuck Ling's talking like he's on stage for a play set in the 1700's all of a sudden.
