Other than Report a problem, you can go to the incubator page and find the creators personally. If you want to contact them...
But they have a looooot to do. And they may even have a life. Not sure. :)
Duo's home page says contact the creators if you have a problem with the course. They recommend the course-specific forums.
I've heard that it's really hard to keep a good motivated team - many people sign up, add a few dozen sentences in the incubator, but when they see the scope of the work in front of them (and that the page saying "you should have several hours a week to dedicate to this" is not kidding), many quit.
So I'm not even sure how many are still active.
It's also a rather thankless job - slogging through literally thousands (I'm sure) of reports, weeding out the dross where people just clicked "should be accepted" even if its garbage, adding the missing alternatives, then the next day, you have 200 more reports.
And the reward? Free-form reports saying "get off you ass lazy developers and fix this problem!!! its been wrong for weeks!!!". Sure, that'll motivate anybody.
The problem with reporting is though:
How should i, or any other novice, know if a sentence is right or wrong?
I am here to learn the language and not to know the language already so good i can spot errors. I only know little bits and pieces and only after i am through i should be able to give decent feedback (not at all good enough to interfere on the backend side). But then i am already through and will go on with my life and try to apply the language.
Many complaints (most reports?) revolve around BrE vs. AmE which is interesting but probably irrelevant for most people that are here.
This course should have declared from the start on which English it is based on and stick with it. Keep it small & simple! Would also remove one extra layer of unnecessary confusion for non native English speakers like myself.
Hungarian is what i want to learn here foremost and there are sentences that are wrong in Hungarian, as i occasionally read comments that say so and occasionally i am fairly certain myself that they are wrong. Some wrong answers are accepted also. And those i try to report and sometimes i possibly get it still wrong.
But reports are worthless, unless native speakers (probably should be experts since discussions also show that right and more right can be close together) plow through every sentence and double check if it means what the translation says and then vice versa again. And so long this does not happen to full extent this course will be "at your own risk"-beta. (though i have no idea how perfect other courses are that are considered ready)
Nevertheless a BIG thank you to all people involved and trying to help.
Beta courses are always "at your own risk". That's what they're here for - to open them up to a broad audience to look for mistakes and discuss the sentences. Being community-sourced construction sites. That's what's been happening for a year and a half now here. (Hungarian and English are pretty hard to translate into each other, gosh.)
If you come across a sentence where you feel that something is wrong, go ahead and report it. Those reports are getting checked by the moderators (who are mostly Hungarian natives) and either added to the roster of accepted translations, or discarded if they're unfitting.
I haven't seen a lot of British vs. American English complaints. The spelling variants (like "colour/color") are mostly automatically accepted, and differences in vocabulary ("pavement/sidewalk") or grammar can be added manually. Duolingo itself tries to use American English on the "teaching" side, but will accept any major variant. (Which is especially fun in the English-Spanish course, where you have about four major dialects of English (British, US, Canadian, and Australian) coupling with many many variants of Spanish (Spain's Spanish, Mexican, Central American, Caribbean, Colombian, and Argentine, to spell out the major ones). That just aside.)
Maybe it is just my impression and much of the criticisms i read are already solved. Many comments are obviously a year old, and i am often visiting the past. Maybe those demanded nursery school teachers already arrived and are accompaning the hundredth Mongolian flying kindergarten teacher ...
I guess a language with many variants of itself paired with any language that has a lot of freedom in word order must be troublesome. I am not sure if English with its relatively strict grammar is then prime candidate for a quarreling couple, if other languages are not much harder to pair to Hungarian.
"What are these glasses like?" would be "Milyenek ezek a poharak?"
Milyen has two modes of using: either you use it in a sentence like an adjective in "milyen [noun]", then it means "what kind of [noun]". Or you have it as a more separate entity in "Milyen/milyenek a [noun]?" with the meaning of "What is the [noun] like?"*