I'm unsure why simply "paradise" isn't an accepted translation. I think this is one of many words where the article is generally used in German and not used in English. There are similar examples where a translation lacking the article in English are accepted but not this one for some reason.
I would partially agree. We don't use the article in English because there is almost no context which would set us up for one. We also don't simply say paradise, but Paradise as if it's uncountable and there is only one. Like "This place is Paradise."
I think it's easy to forget it can be used as a noun with an article since we almost never need it. "Which one did you say was a paradise?" "That one! That's the paradise."
That being said, since this is in the religion section for me so I would assume that Paradise with a capital P would be accepted.
In English, especially when capitalized, "Paradise" was another, old-fashioned way of saying Heaven, or the afterlife based on oneness with God and being in his favor (not unlike Eden). In that sense it's not a place above the clouds (which I believe comes from heaven getting mixed up with aether). You will particularly see "Paradise" in translations of Islamic stories, but others too. Heaven is a synonym and should be accepted.
The legendary Garden of Eden was a "paradise" in a literal sense.. "Paradise" comes from a Greek word meaning an enclosed garden, which came from a word in an old Iranian language (Avestan) with the same meaning. A walled garden in desert lands would naturally seem like a "paradise" in the modern meaning of a beautiful, marvelous, even "heavenly" place.
I think "der Garten Eden." is the most used phrase with "Eden". "Diese Gegend ist ein wahres Eden." can be said, but "Eden" can easily changed by "Paradies".
The word "Paradies" will be understood much easier. "Eden" is a word mentioned in the Bible. "Eden" is also a word used in "gehobenem Deutsch". - Not everybody uses/ knows "gehobenes Deutsch". "Paradies" is a word which is known by everybody. Because "Eden" is a word of more formal German, it does not fit to/in every situation.
I can think of three possible meanings for this word in English: an earthly parallel to heaven, like Eden, mostly used metaphorically; a slightly old-fashioned or poetic description of the Christian Heaven itself, unity with God and freedom from sin and its effects; or the Muslim Paradise. Is the German word also this flexible? Could I use it in any of those contexts as well, or is it specific to one religion or concept?
"Das Paradies" has all these meanings, too. This term includes all concepts - religious or not - of a place that can only be reached by the good and/or where there is only good for you. So this term is used for heaven, eden ect. as well as for some holiday resorts in corresponding advertisements. (The buddhistic concept of "Nirvana" is not included as its key ideas do not revolve around luxurious or carefree living but the merging into nothing and everything that contradicts the lingering of an individual in his individual feelings of happiness or whatsoever.)