难题的问题在英语中可以翻译为 "The problem of the difficult issue" 或者 "The issue at hand". 如果更口语化一些,可以说 "The tough question" 或者 "The problem question".
The translation of "难题的问题" into English would be "the problem of the problem" or "the issue with the issue." However, if you're looking for a more natural phrasing, you might say "the difficulty of the problem" or "the challenge presented by the issue."