Translation:He hates beef because he is a vegetarian.
Apparently you like to rant on. None of my friends was alive in 1842. Several of them were educated through Irish to post graduate level. Foras na Gaeilge doesn't support one term over the other. It is not a dialect choice until recently the only choice was feoilséantóir'. Arguing that a term that is clearly based on a wacky version of English is more "modern" and should replace the existing word; in spite of the native speakers preference is ridiculous.
You're the one complaining about the words that Irish speakers use, based on the opinion of one or two people whose only qualification is that they claim to speak more Irish that you do.
I also didn't make any claims for "veigeatóir" simply of the basis of it being more modern. I simply pointed out nobody will every seek to claim that "veigeatóir" is anything but a modern term, but that, because it is a positive term, describing what vegetarians do, rather than a negative term, describing what vegetarians avoid, it's easy to see why vegetarians would adopt it, and that, even if "feoilseántóir" could actually be attested to from centuries ago, as you claim, that doesn't make it a better translation for a word that was only coined in 1842.
The correctnes of translations aside. The sentence is making a statment that is factualy incorrect. As a vegetarian, i still liked beef, I just preferred not to eat it. Rearranging the sentence to - He is a vegetarian because he hates beef (and inferring other meats) would at least make some sense
It is no more or less factual than any other statement on Duolingo. You aren't the only vegetarian in the world, and some vegetarians do hate beef, and there only has to be one beef-hating vegetarian who ascribes their hatred of beef to their vegetarianism for this statement to be true.
As feoilséantóir is a word that long predates the word "vegetarian", it's not accurate to say that feoilséantóir is the Irish for "vegetarian".
Many vegetarians who consider vegetarianism as a positive choice, rather than a penitential avoidance of meat prefer the positive term veigeatóir rather than the negative term feoilséantóir.
When you say "people who don't like Béarlachas" you mean people who would be happy to see Irish die out entirely as a spoken language, as long as it dies out "pure".
focloir.ie is a "descriptive dictionary" - it records the language as it is used, rather than simply describing how some people think the language should be used. The choice of "veigeatóir", which focuses on the positive aspect of what a vegetarian favours, rather than "feoilséantóir", which focuses on the negative aspect of what a vegetarian avoids, while also acknowledging that "veigeatóir" is a modern term, is a perfectly reasonable example of how a languages grows and evolves. It allows for the next step "vegan". In this way, it isn't actually an example of Béarlachas, because it was actively adopted because it was a better fit than the older term.
As it happens, the only vegetarians I know don't speak any Irish, but I can see why Irish speaking vegetarians would prefer to use a positive term rather than a negative form to describe themselves, just as they have made what they consider a positive lifestyle choice, even though many of the rest of us might see it in negative terms.
So tell me, John, what do you and your Irish speaking friends do when you don't have the vocabulary to express an idea or concept in Irish? Do you turn to a current dictionary to look it up, or do you make up some portmanteau word from the limited vocabulary you already have?
How would you order Avocado toast, for example, or order an exhaust manifold for your car, or install a new web browser on your computer? Or do you have a cutoff date, and just don't use words that weren't used in Irish before 1950, or 1900, or 1850?
I order things in English because that is the language of the country I live in. My Irish speaking friends say whatever they want because they are fluent. When they say they wouldn't use veigatóir I believe them. If you think the Irish are too primitive to have words for things that have existed for centuries maybe you are the problem!
So how many fluent Irish speaking friends do you actually have, John? 2? 5? 20? 50? Do they reflect the differences between the dialects? How many of them are vegetarians? What makes them more reliable that the people working for Foras na Gaeilge or Scoil na Gaeilge in DCU?
"Vegetarian" was only coined in 1842 in English, and "Vegan" in 1944. It's entirely possible that the notion of a "meat denier" existed in Irish before that (given the significance of dietary abstinence in Catholicism), but that doesn't mean that "feoilséantóir" is a perfect match for "vegetarian", and it provides no basis for new developments like "vegan".
And I'm afraid that if anyone is treating Irish as "primitive", it's people who refuse to move with the times, and adopt new terminology as appropriate. Sometimes that new terminology will derive from existing Irish terms (féinín for "selfie", for example) sometimes it will involve a borrowing from English or some other language ("tae", "raidió", "bus"). But when someone insists on "gluaisghuthán" instead of "fón póca", you've got to wonder.