non-British-English “tells” in fanfic?

I know us Dramione peeps are very detail oriented when reading fics, and I noticed some people commenting about “tells” that the writer doesn’t use “proper” Dramione language or British English.

Aside from some obvious ones like arse/ass or gods/God, what are some tells you’ve noticed when you read or pay attention to when you write to preserve Dramione?

I’m curious to hear your thoughts as I feel like I subconsciously don’t notice them when I’m focusing on the plot/dialogue :)

Doesn’t have to just be words, could also be cultural things (ex. correctly writing tea scenes or little strays away from canon language)!