Worth noting for non-native English speakers. Data can be a plural noun (multiple datum = data) or a "mass noun" where it is a singular noun that represents a multitude. So "These data are good" is just as acceptable as "This data is good". This wiki article might explain it better than I did:
There is a difference between interpretation and translation. In general practice/principle it is far more important to interpret. To not have Duo mark you wrong you are safest to just translate. Duo isn't perfect, but it is much better with translations than interpretations.
Without context it's more likely to mean data like information.
The plural of date (Datum) and data (Daten) is the same. If you mean information ("Daten") there is no singular for the word in German. The plural of Datum is Daten for every case (accusative, ...).
It is really rare that I hear someone saying "Daten" for different dates. If I heard it, I also heard the question "What is the plural of Datum?" before. So at least where I live it's uncommon.
"This data is good" or "These are good data" works in my mind, but not "These data are good"... Sounds like something uttered by a foreign scientist that doesn't have English as their first language. I'm an American computer repair expert with my own shop, been working in the field for more than 20 years, and this translation sounds like garbage. I deal with data retrieval on a near daily basis.
99% of every native English speaker I know in Britain uses the word data as a sungular collective noun, and this includes a lot of technically trained people. They would and do say "This/That data is good. Duo needs to rethink this question and answer. This query was first raised 6 years ago. Surely the problem should be resolved by now, or are these posts simply not monitored. If Duo thinks it is grammatically correct, it should at least pin a justification to the top of this thread
It's pretty confusing to have a sentence talking about the plural of datum (a point of information) in a lesson teaching about dates (points in time). I understand the plurals of date and datum are the same in German, and know that the sentence makes perfect sense regardless, but still.
Because in English (at least in the US) the word data is most commonly used as the singular and not plural, depending on your context and duo (from what I've seen) tends toward using the translation that is most common in everyday conversation. This is a case of the German being more precise than the English.
So, how can you tell if you're a foreigner learning English? Generally speaking:
--If you are doing research/technical writing, it's always "These data are good." with data being plural. This is probably the only time you'll see an American use data as a plural word and paired with "are". (Unless they are a research scientist and it's become habit.)
--If you are talking to someone on the street it will typically be stated as "This data is good" with the assumption being that you are talking about a set of data points rather than a single piece of data (a datum) even though you are using the singular "is". This is what is called a "mass noun". (see the link from the top poster for the wiki page)
I will say, I put "these data are good" and duo accepted it, so as long as you make sure to use "are" instead of "is" in your translation, you should be fine making data plural.
Hope that helps. :)