To hopefully put an end to this more or less frivolous discussion, I will point out that, having read the book, the novel spans exactly one waking day of Ivan Denisovich Shukhov, "from reveille to lights out." Therefore, I would say that the proper and only acceptable answer is "One Day in the Life of Ivan Denisovich," Russian's lack of articles notwithstanding.
Are you saying that the meanings of "A" and "one" aren't the same?
"A" is a singular pronoun.
You couldn't ever say "A" followed by some form of the word "day" and have it be talking about multiple days.
I have seen it written both ways (there are over 11,000 references to "A Day in the life of Ivan Denisovich" listed on google)...I think it should be correct but luckily it didn't matter.