This is an example of a very particular kind of sentence: http://en.wikipedia.org/wiki/Dative_construction#German
I can understand that Duolingo sometimes shows information that hasn't been properly taught. However, try not to find the grammatical correctness of the sentences by translating so literally, because you'll find a lot of trouble. The good thing is that the community helps a lot with their comments, so can better understand the concept and how to use it rather than just translating it.
There is no such thing as a "dative adjective" in German. A noun/pronoun will be in the dative case because of either its function in the sentence, its relationship with a verb requiring the dative case (ex. danken), or its relationship with a preposition requiring the dative case (bei, mit, etc.).
In this sentence, it is like we are saying "it (the weather) is cold (to) you". That 'to you' is the reason for dative 'euch' and 'Es ist/Ist es'.
The verb is modifying the subject "it" (es), which is left out here, so "ist" is correct. Euch is never a subject... Ihr could be... ...similar to what mfcabrera said above... the Duolingo text,"Es ist euch kalt.", is turned into a question, with the "es" dropped. Anyway, the Duolingo text seems really weird to me. I'm pretty sure that some Germans (improperly) say "have" in this situation. So, "Ich hab kalt." instead of "mir ist kalt". So you could ask a group of people, "Habt ihr kalt?", which is much easier to pronounce than "Ist es euch kalt?" IMHO
What I can get from your reply is that the sentence "Es ist euch kalt" is something like "Is it cold for you?" referring to the weather; I don't know if I'm wrong. Comparing it to Spanish, I think it would be like: "Para ustedes, ¿hace calor?" (Imagine some people from a cold place are visiting someone who lives in a tropical area; the host would ask this. This question would be valid in Spanish).
And just like Mauro, it's pretty good that you pointed out the supressed "es".
Euch can never be a subject, so it will never match up with the verb. This is an idiomatic construction so it can't be translated word for word. Think of it as a vocabulary word instead of as a sentence and learn the entire phrase as is. Mir ist kalt, dir ist kalt, ihm/ihr/ihm ist kalt, uns ist kalt, euch ist kalt, Ihnen/ihnen ist kalt. As has been noted, this idiom should be in the dative pronouns section. Has anyone else reported it as a problem?
Dative, ah, Japanese handles it so much easier than German! Already being bilingual i've learned that your target language always handles an idea/concept with a different part of speach. In this case, weather affecting a person occurs in the dative, English the nomitive, Japanese can be both. What other unique situations are handled with the dative case in German that are nomitive in English? I know English teachers stab you if you use the dative (passive) case in papers...have we sorta killed our dative case or what?
Well, no, the English dative case is governed by to/for, not by, so I doubt we've killed it (jury's out on the instrumental case though - the usage of by and by means of has been far outstripped by the usage of use + direct object + to do X).
Fun fact: in most Indian languages are the words for feeling the weather represented by a single verb and a genitive target. Imagine the horror of such a thing in English: "it colds my." I'm shuddering.
It isn't accusative, it's dative. The sentence is actually incomplete (but is idiomatic, meaning you can still use it and make sense), and the full sentence is "ist es euch kalt?" (= is it cold for you). Euch is the dative form of ihr, which is the informal and plural you. Formal would be "ist Ihnen kalt?" (with the capital I - Ihnen is the dative form of Sie, the formal you).
First note: haben conjugates as follows: ich habe, du hast, er/sie/es hat, wir haben, ihr habt, sie/Sie haben. To answer your question, your meaning would most likely be understood, but the correct way is to use the form of 'sein (ist)' with the implied object (the weather), the dative pronoun (mir, dir, euch, etc...) and the state of warm or cold.
I saw this link in the discussion. This link showed up http://en.wikipedia.org/wiki/Dative_construction#German but here this sentence is with Dative, so what case should be used?
Because Duolingo sticks sentences in which don't quite fir the theme of the lesson - for review, to keep us on our toes...
Oh dear, I've not come across euch before and I'm not ready for it yet either! I've just got into plurals as Duolingo asked a question I didn't know the answer to so I Googled it and it said "uns ist kalt' for "we're cold". I don't know why it isn't Wir sind kalt? When Duolingo comes up with something which hasn't been covered before, then I go looking for an answer. I'm hopping around all over the place looking for explanations for just about everything and get more and more bogged down. This isn't a complaint, just a matter of fact. I'm really grateful it's free and it's wonderful how helpful people are on this forum. I know my grammar doesn't have to be perfect, and I'm only at the very beginning of learning anyway and probably it would be best just to accept what I see written down and not delve any further! Thanks to anyone who may help me with the "uns ist kalt".
Okay, so a lot in here: First, a good place to start with any new lesson group might be to use the website version of Duo (as opposed to a smart phone). When you click on the lesson (ex: Dat. Pron.) and then click on the light bulb icon. This gives an overview of grammar and/or vocabulary covered in the unit. Granted, it may not prepare you for every single word, but it will give you a lot of good answers or things to watch for before you dive in. Also, read through discussions on phrases you find tricky - usually someone has had your same question and people have answered it if you read through.
Second: To 'be cold' is an English way of saying it. In Spanish you 'have cold (tengo frio)' and in German '(it) is cold (to) you (es ist dir kalt -or- dir ist (es) kalt). The tricky part here is that this 'to you/me/us/them' is in the dative case (more advanced than beginner). So in German, we are not cold (unless we're cold-hearted or frigid), but rather it is cold to us = uns ist kalt. The word 'euch' is the dative form of the plural you (you all, y'all, you guys). This is not easy stuff, so try to be patient with yourself and the program as it comes up.