As for me, I am trying to speak and write British English, so my websites/apps usually feature the UK flag (the pic is taken from my homepage)
@NickKaramoff If you use the American flag you have to make sure it's at a 1st grade reading level! I kid. But seriously Americans are used to seeing the British flag as representing English. You wouldn't have a Canadian flag for French, would you?
Fosstodon is an English speaking Mastodon instance that is open to anyone who is interested in technology; particularly free & open source software.