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. :)
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?
Sabine Bergmann- thank you. Indeed I would prefer a duolingo-course turkish-german. But unfortunately it is not available. So I have to learn two languages together / the same time. And so I am often looking onto the online dictionaries like beluka and langenscheidt. If you are looking for the german translation for “insan” on beluka you can read: human, person and some more....
Duolingo, a great programme for all of us, is used by many people which are not native English speakers. My English also is not the best and I am surely making a lot of mistakes. I have no other choice to use "Turkish for English speakers" as there is no tree "Turkish for German speakers" for example. I am doing my best to understand all things explained in Tips and Notes and in discussions. I am trying to help others if I am able to do it and many others are doing that. But instead of simply answering the question, which answer you may know, you say "Learn English first." That is rude and not helpful at all. Better you would not have given any answer if you really think that only those people may learn Turkish who are speaking and writing perfect English. What would you have thought if you get such an answer of any of your questions. You may surely have a lot of questions as you are on low level of any of the languages you try to learn. Hopefully the day will come that one of your questions will be answered this way. Have a great day!
Sometimes it is also easier or makes more sense through a different language. For example, English is my Native language but I prefer to learn Portuguese and Italian through my second language, Spanish, because they are much more similar in all aspects, including grammar and vocabulary. It is much easier for me to learn that way but sometimes I have questions about the Spanish part of it.