今天是星期五用英语可以说是 "Today is Friday." 来源是英语每周的第五天叫做 "Friday"。下面是一些例句：

Today is Friday. 今天是星期五。

I'm so glad it's Friday! 我真高兴今天是星期五！

Let's go out tonight – it's Friday after all! 咱们今晚出去吧，毕竟今天是星期五。

Friday night is movie night at our house. 星期五晚上是我们家的电影之夜。