If you thought that the Aussie and Kiwi flags were similar...take a look here!El Salvador and Nicaragua not only have similar flags but similar coats of arms. This is partly due to when they were united in the very short lived in the 'United Central American States.'
Unity can sometimes be a very difficult thing.
Nicaragua
Close up of El Salvador Coat of Arms
Close up of Nicaragua
Coat of Arms
Both have the triangle, glowing liberty cap, rainbow, and five islands.