No, it's okay. In most contexts I'd say, "the people there are very happy," but sometimes the sentence works better with "the people who are there." I can't think of a situation where either version actually sounds wrong, so I think they're pretty much interchangeable.
(To me, "the people who are there are very happy" sounds a little more like it's emphasizing a short-term location. Like, "the people who are at the restaurant right now are very happy." And "the people there are very happy" sounds more long-term: like it's talking about where they live, or where they work, or something. So I think that's how I choose which one to say, but it's not a rule of English, or anything. You could use either "the people there" or "the people who are there" all the time, and you wouldn't be wrong.)
In English you can sometimes omit the relative pronoun.
"The people [who are] there are very happy." "He has the book [that] I want." "The bed [that] they slept in is very comfortable."
Some languages will allow you to omit it, and some will not...like French for example.
The sentences are identical in meaning and a lot of people omit the relative pronoun where they're able to which is why it might sound like the more natural one...but both are equally correct. :)
Peace to all. We need to be patient with each other, at tge same time we need to forgive for small lapses in manners or language, after all we are duolingoes, people out to study other cultures and languages, we may be the people who will in the future stitch all the hems and seams of differences in the varied human cultures. We maybe the ones to teach humanity to accept cultures as is instead of trying to change them to reflect our own. For that we need patience, understanding and love for our fellow human beings.
The English translation uses a relative pronoun "who" and there is a Rel. Pron skill in which the Turkish counterpart -(y)An is taught, but I think you can't say "Oradayan insanlar çok mutlu," right? I suppose -ki is used with nouns and pronouns, but -(y)An is used with verbs. Is it so?