Probably nothing grammatically but "facts" is a poor translation of "Daten". Data implies a routine collection of bits of information. Facts implies some special importance or meaning in some context. Most significantly, data can be wrong (and often is). Facts must be true, by definition.
If a "fact" turns out to be wrong, it was never a fact. And that's not just data, THAT's a FACT! :-)
The noun das Datum refers to both the date as in day of the year and a single piece of information in IT, even if the information meaning is almost always used in the plural. So technically the translation could be both dates and data.
But persönliche Daten is almost exclusively used in privacy etc. So I would assume it to be personal data unless you're concerned with the privacy of dates.
I have no problem with "personal data" but I do not understand the grammatically incorrectness of "These are".... personal data". For us to reconcile this as grammatically correct it should read "This is"....but the answer that comes up says that it is "These are"... sounds so wrong. Can anyone explain this to me? Thanks!
DATA originaly is a latin word and plural so the correct answer would be "are" and not "is" . But in the english/american language it has a little bit another meaning than in Latin and data is more a "package of information" thus that people often say: "this data is personal" instead of "these data are personal". SO in the English language DATA is NOT a plural word. so Duolingo has an error here. I agree.
It is a plural and is used as a plural when looking at say a graph or diagram, you would say "these data show an increase in price" for example. You could hear "these data are personal" in Britain but it is becoming less common. Both should be (and are) excepted by Duolingo. I can't comment about American usage.
"Data" like "dice" is a word that is technically plural, but is commonly used as singular, and many if not most native English speakers are unaware that these words are actually plural. The singular verb should be permitted because of common usage. You will hear people saying, "This data shows ... " or, "This is a lucky dice."
Similarly you will hear people saying, "This is a difficult criteria," or, "Television is an interesting media." You will even hear this pluralised as in, "TV and newspapers are different medias."
It's just one of the many strange exceptions to a rule in the English language. FreekVerkerk is correct in saying that it's treated more like "[this] package of information", but English does have the singular version of data (datum). I have, however, rarely heard it used outside of professional/academic conversation.
It may even come up in conversation like debating what the correct plural of octopus is or some other bit of grammar that has mutated over time.
The discussion above answers this. But simply, "data" is a group of many pieces of information. German treats this as a plural: das sind = "these are", but English treats it as a bulk noun: "there is a lot of data" ~ "there is a lot of sand", NOT "there are many sands in my shoe".
Please let me know if this needs more explanation.
Here, this rule is applicable: Foreign words -/en with modified stem in the plural
Note that there's not one inflection pattern for plural -en but many.