"He does not eat pork, because he is vegetarian."
Translation:Li ne manĝas porkaĵon, ĉar li estas vegetarano.
I have heard "I am vegetarian" and "I am vegan" many times. Judging by the number of google search results for these I don't think they are uncommon.
He isn't saying that way is uncommon. But rather "Mi estas vegetarana" == "I am vegetarian" and "mi estas vegetarano" == "I am a vegetarian". He was simply pointing out that we are translating an adjective to a noun, instead of a noun to a noun
Mia kulpo! Ial mi tute miskomprenis ŝin. That said, different languages have different ways of phrasing the same thing so I don't think translating an adjective to a noun or vice versa is inherently a problem. (We don't say 'is cloudily' for instance :)
Wouldn't it be possible to leave out the second "li"? I thought it was possible to ommit the second personal pronoun, if it's already stated earlier in the sentence.
“... li estas vegetarano.” means “... he is a vegetarian.” not “... he is vegetarian.”. In the English sentence given, the word “vegetarian” is an adjective describing him. It is not a noun.
It is interesting that I cannot report this, presumably because Duo accepted “vegeterana” as a typo rather than as a mistake.