"Selamat idul fitri."
Eid al-Fitr (/iːd/ eed; Arabic: عيد الفطر ʻĪd al-Fiṭr, IPA: [ʕiːd al fitˤr]) is an important religious holiday celebrated by Muslims worldwide that marks the end of Ramadan, the Islamic holy month of fasting (sawm).
Eid is known in Indonesia as Hari Raya Idul Fitri or more popularly as Lebaran, and is a national holiday.
There is no option for "happy" in the test method version where words are prefilled and moved by the user. The only provided words are: "Eid", "greetings", "and", "thank", "much", "mubarak".
On gettting this question wrong it gives the answer as "Happy Eid ., Happy Eid al-Fitr." which makes this question difficult for new learners as that's not a possible solution with the options given and no real context is given in the English translation for the user to guess something similar.
Needs review I think?
If you are using the web version there should be a 'use keyboard' button that allows you to type the answer yourself. On the mobile app, however, you are quite correct (or you will be when Indonesian is ported to the app), and people unfamiliar with this greeting might well find it unenlightening.
I have noticed that the possible correct answers enabled by the tiles do vary between different practice sessions, however, although I don't know quite what determines the weight given to different translations.
"Eid Mubarak" is the greeting you say to others to celebrate Idul Fitri (also called Eid al-Fitr in other parts of the world). Idul Fitri celebrates the end of Ramadan for Muslims, and is a time (usually 3 days or so) for Indonesians to "mudik" (literally "swim upstream", but here means to go back to your hometown) and gather with their family members and celebrate.
I think it would be best if the lessons were completely secular. Muslims do not greet foreigners with Muslim greetings. Hindus do not greet foreigners with "Om Swastiastu", or "Selamat Galungan". Let's take religion based lessons out of DuoLingo. Put that training in the mosque, temple, or church, where it belongs. It doesn't belong in an app that people are using to learn how to order food in a restaurant, or to ask where the restroom is.