"Helaas kan ik helemaal niet dansen."
Translation:Unfortunately I cannot dance at all.
Okay, I tried it because I thought this was not a false cognate. I still think that "Alas, I cannot dance at all" should be accepted. While not frequently used, the expression "alas" IS used. (Perhaps it's because they wanted an adverb and not an interjection--which I get-- just that helaas seems to fit alas so well!
Well, you said it yourself: "While not frequently used..." and that is probably the reason why "Alas" is not an accepted translation for Helaas. You have to remind yourself that this is a beginner Dutch course and as such the English translations should be what is most commonly used in spoken language. Also, not everyone taking this Dutch course is a native English speaker and those people may be very confused by words like Alas. (Now that I look at it, Alas does look rather similar to Helaas and I'm wondering if it wasn't derived from that word, you know, like the word Yankee was derived from the Dutch name Jan-Kees).
Taught history for many years; but I remember one of my earliest library books (around 3rd grade) was a biography of Peter Stuyvestant. I've had an insatiable curiosity ever since on the many Dutch influences in the area that was once New Netherlands. Many find it difficult to realize just how much (particularly but not exclusively) the areas around NYC retain Dutch influences (The Holland tunnel, Harlem, -- and then there are the Hudson (Catskill) areas which still retain Dutch names. Funny how you remember these things.
I agree with OnkelD that 'Alas' is a good fit, and it was the first response that came to mind. But then I thought that it was unlikely to be accepted by Duo, and substituted 'Regrettably' instead, with the same result - not okay. Personally I think 'Alas' should be accepted -- despite it being a bit of an archaic word, it seems to be not infrequently used. I plugged 'sadly' 'alas' and 'regrettably' into Ngram Viewer, which indicated that in 2008 the occurrence of 'alas' was more or less midway between the other options (tried to paste the output from Ngram, but could not).