Duolingo has just released Latin as a language to learn. Here is the flag they ended up using: 
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[![latin flag][1]][1]


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Here is how it looks in the app:
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[![Screenshot from Duolingo app][2]][2]


  [1]: https://i.stack.imgur.com/fbfoi.jpg
  [2]: https://i.stack.imgur.com/aaa3q.jpg