I don't see any similarity. CH/ch is the one and only abbreviation used about everywhere. Which other one would be used by whom? The letters might not be obvious to any speaker of a living language. But that's intentionally I understood. They have several national and egen more local languages, so they chose an abbreviation from Latin.
GR/gr is ISO for Greece, but EU uses EL/el the previous commenter wrote. The latter seems to come from Greek language, although then spelled using the Latin alphabet
How are those cases similar, except for it's not obvious to the average English speaker where some letters came from?
