When it comes to expressing dates in English, there are specific formats and nuances that can sometimes puzzle non-native speakers. For instance, if you're wondering how to say "9月21日" in English, the answer lies in understanding both the numerical and written forms of the date.

In English, the date "9月21日" would be expressed as "September 21st." Here, "September" is the name of the month, while "21st" indicates the day of the month. The suffix "-st" is used because the number 21 ends with a '1,' which typically takes this suffix in English date expressions.

It's important to note that while some languages use a different order for the day and month (such as "day/month/year"), English commonly follows the format "month/day/year." Therefore, when writing or speaking about this date, you would say "September twenty-first" or simply refer to it as "the twenty-first of September."

Understanding these conventions can help ensure clarity when communicating dates across cultures and languages. Whether you're writing an email, preparing a presentation, or just chatting with friends, getting the date right in English can make your communication more precise and professional.