Check this out if you're interested: https://www.youtube.com/watch?v=sTzp76JXsoY (Tom Scott, 3min, "Why Do Flag Emoji Count As Two Characters?")
Or even more in depth: https://www.youtube.com/watch?v=mubfp9WYvvI (Jennifer Lee, 55min, "Emoji by the People, For the People, a CS50 tech talk")