So what does it actually mean in English? "Do you eat again?" is poor English unless qualified such as "do you then eat again at 4pm?"
Google "Do you eat again?" and you'll be surprised how often that phrase is used.
That's misleading. If you google with quotation marks surrounding it (to look specifically for that phrase, as opposed to the individual words), you only get 16 results. Googling the Irish sentence "An itheann tú arís" yields even fewer results: 1 (this very page). On the other hand, the present progressive equivalents, "Are you eating again" and "An bhfuil tú ag ithe arís" yield, respectively, 19,800 and 40,500 results. So although I understand the point of using this sentence to illustrate the usage of an adverb, it may be doing more harm than good to introduce it in this way -- learners of Irish may think that this is the way to ask "Are you eating again," when in fact Irish speakers also use the present progressive. Duolingo should introduce this form earlier: Rosetta Stone introduces it almost from the very start.
16 results is good enough. Don't forget, this is not a course in English stylistics. It's an exercise in basic Irish. The simpler the better. Just correct enough to ensure understanding. Almost word for word. Just the way it should be at the beginning.
Would that sentence make any sense to an English-speaking person? I haven't a clue as to its meaning and nor has anyone else I have asked. From my point of view, I feel the vocabulary and the grammatical points would be more easily understood if the sentences were more coherent.
Irish, like English, has a distinct way of expressing the present continuous, so it wouldn't be correct. In fact, this sentence is also weird. "Do you habitually eat again?"...
I can't imagine that "Do you habitually eat again?" is grammatically correct in any language.
Would it work if the listener was sick and not regularily eating and now the speaker is wondering if they're eating regularly again?
Is "arís" another compound word and that is why it ignores the sws-bwb rule or ia it just an exception?