“与题目不相干”可以翻译为 “irrelevant to the topic/question” 或 “not relevant to the subject/issue at hand” 。
例如：
This point is irrelevant to the topic we're discussing. （这个观点与我们现在讨论的题目不相干。）
Your comment is not relevant to the subject at hand. （你的评论与当前题目不相干 。）