"¿El concierto es el martes?"
Translation:Is the concert on Tuesday?
"Es el martes" I think it's wrong. The correct should be "es en martes... isn't it?
No, "en martes" does not work here. That would mean "on a Tuesday".
"On [weekday]" translates to "el [weekday]" in Spanish, since you're talking about a certain day.
Why isn't the name of the day capitalized? Tuesday or martes should be capitalized, right?
It's not a proper noun, at least in Spanish perspective. Days of the week come back every seven days.
No, that doesn't really work, for two reasons.
Spanish doesn't like to do subject-verb inversions in yes-no questions. Such a question usually looks just like a statement, but framed with question marks.
Spanish doesn't like to put two nouns (or noun phrases) right next to each other. If possible, you usually have some buffer in between two nouns, like a preposition or a verb.
the voice recording for this sentence is very poor. there is no indication in the tone of voice that it is a question and not a statement. if I were not looking at the text and could see the question marks I would have translated it as "the concert is on Tuesday" not "is the concert on Tuesday"