Is there an article missing in the English translation, "It is already the weekend" or "It is the weekend already"?
You'll find "it is already weekend" a lot if you search for that phrase, but to me it feels as if it was written by someone who is not a native speaker of English.
The German version sounds perfectly correct to me but in my English, it can only be "the weekend" in this context.
As a learner of the Hungarian language, I appreciate seeing what the Hungarian means and why. The definite article may be appropriate in English but should not be required for a Hungarian language course. ...unless duolingo is trying to be an electronic phrasebook rather than a language learning tool.
The problem is that the English speakers get the answer wrong when it asks us to go from Hungarian to English because we expect the article. Such issues are why they require people who are fluent (or nearly so) in both languages for helping develop a course. "Purpose of the course" is not an excuse to not get it right for both languages.