Another one I've noticed is using "I've" as a contraction in e.g. "I've a meeting to attend". Seems totally reasonable but for some reason native speakers just don't use it that way.

Could also be French speakers. They would say "J'utilise le format .avif depuis quelques années." I think the "depuis" throws off the French speakers when they translate that literally as "since some years" instead of "for some years".

Another common tell: I wake up in the morning in the US/Pacific time zone, and see the European writers on HN using "I have ran" instead of "I have run".

German speakers usually have very good English, but this is already one of their tells.

Fixed that for you.