You have a good point. However, I am conservative on Type 4 fu'ivla in that I believe
they should only be used for words that are internationally recognized. 'Ramadan'
is recognized virtually everywhere, whereas Eid ul Fitr is not. I'm tempted to
suggest musysezyfantyfamnunsla - but that's just too long!
I think it's best to take a hint from Moslems themselves. What do non-Arabic-speaking Moslems call these holiday? Do American Moslems call it "Eid-ul-Fitr" or do they call it "breaking the fast day"? I believe the former, so this is what Lojban should do as well.
I don't doubt that "Eid-ul-Fitr" is the term most often used by the world's Moslems. But not so in Indonesia, the country with the most Moslems in the world, where it's Hari Raya Aidilfitri","Hari Otak", "Hari Raya Idul Fitri" or "Hari Raya Puasa". In Nigeria "Small Sallah". In Turkey "Bayram".
I guess I'll leave this one for someone else to figure out.