The tea is nice - accepted 24 Aug 2014.
Dutch is so close to the Afrikaans with which I grew up here in South Africa. As a result I could be approaching this from a different viewpoint. I have found dozens of my translations being accepted by Duo even though my answers have not been the 'official versions'.
Should I continue to post these alternatives here - or do they merely add to the clutter?
Example - De thee is lekker (Dutch) = Die tee is lekker (Afrikaans) = The tea is nice.
It's accepted as a translation of the German lecker, so it's appropriate for Duolingo to accept it for lekker as well. If you're not a native English speaker, just know that "yummy" is a bit of a child's word, and you might sound juvenile using it. Otherwise, it's perfectly acceptable and you should report this to Duo.
German lecker and Dutch lekker aren't really equivalent, though. The German word is still much more restricted in ways that are suggested by its original meaning of lickable/lickworthy. Yummy is usually a pretty good translation for German lecker, but very often inappropriate as a translation of Dutch lekker.
That may have been part of it, but the Germanic people were well known for their trading and exploring, and the Germanic and Hebrew people were more or less neighbors. The extensive trading resulted in a fair bit of trading more than just physical items, but culture and language, as well.
Some background: The Dutch word lekker and its German cognate lecker are derived from the verb lekken/lecken (to lick) and originally described what is pleasant to lick. In Dutch the word was generalised to the point that nowadays it means little more than good. In German it has pretty much preserved its original restricted meaning of tasty, and in the south most people don't use it at all.
A few years ago, a Dutch electricity company advertised its electricity in Germany with big billboards saying in Dutch "Lekker Strom". This is supposed to mean good electricity in the sense of good for the environment. But German speakers read it as tasty electricity, and the resulting comic effect was no doubt intended.
Yes 'hartig' means 'savory'. I've never heard it used as a character trait as people tend to use it to describe food, but it's true that technically 'hartig' also means 'hearty' (as 'hart'='heart' and the suffix '-ig'='-y') although if you would describe someone as 'hearty' you'd probably use the word 'hartelijk'
My dictionary gives me nice, good, tasty, delicious as translations for lekker. Johaquila (hi) gives lekker as being little more than "good" these days. The dictionary definition seems to offer a wide range of meanings from the fairly bland nice to the ecstatic delicious. This is not really satisfactory. How do I tell a hostess that her meal was "delicious!" rather than merely "nice"? And does lekker really span the range from nice, ok to fantastic?