It is slightly different. "... are long days" vs "days are long"
You will find this difference in many sentences and we generally distinguish this.
Hm, difference is not "are long days," it's the allowable and flexible use of "here," which clarifies place but can be used flexibly.
Sorry, you are right. I must have misread one of the sentences. Now the question is whether we have "(days here) are" or "days are here". I am not sure if that is a difference or not.
As a native AmE speaker, I don't feel any meaningful difference between "the days are long here" and "the days here are long." I've added the latter as an acceptable alternative.
I agree with Cenicera. If one is in a northern latitude, saying 'In June the days here are long" makes great sense, for example. Since multiple translations are permitted, I also recommend this one.
"We have long days here in June" should also be accepted, means the same thing.
Although the ultimate meanings are very similar, I would not recommend adding this translation, since the original sentence is about the days "being" long, not about someone "having" long days. IMO, translations that are closest to the original sentence -- regardless of whether the original is Czech or English -- are usually best, unless they sound extremely odd and need some tweaking in the target language. That's not the case here, but I will defer to the CZ natives on the team if they feel that the addition would be appropriate.
If you just left the comma out of your answer, Duo should not have rejected it, as punctuation is normally ignored. Did you use the Report button? If not, we cannot tell you what might have been wrong with your answer.