私のビザの有効期限は2018年3月18日までですって英語でなんて言うの？

Another way to talk about the validity of something is to mention when it expires. This is simply another way to answer the question. I hope that this helps! :)

If asked about the validity of your visa, you can use any of the above-mentioned expressions: Subject(your visa) + Is + valid + until (followed by a date) OR Subject + "expires on" (proceeded by a date). The expression "expires on" changes to "expires in" when you are only referring to the month.

E.g., My visa expired in May, 1954
My visa will expire in March.
My visa expires on March 18, 2018

I hope this helps:)

"Expires" means is no longer valid and can no longer be used. So, the day that your visa is valid until, is the same as the day that it expires.

"My visa doesn't expire until..." indicates that your visa is valid and operational up until the date of March 18, 2018.

"The expiry date" indicates that there is a specific date at which point your visa is no longer valid. After this "expiry date" your visa is "expired", is no longer valid, and needs to be renewed. The term expiry date can be used for things such as visas, food, drinks, policies, contracts, documents, etc. It is most often used in reference to food or legal documents.

Since 2018 is already over, I chose to phrase the first two answers as simply, "March 18," in case the speaker actually means that their visa expires this month in 2019. In English, it is important to note that, "until" means a condition that currently exists and will continue to exist until a certain point in time, rather than a condition that has not yet begun. However, if the speaker meant to say that their visa had already expired in 2018, the final sentence expresses this.

When asked when your visa is valid until, and you want to explain that it is valid until March 18, 2018, you can use one of the abovementioned suggestions.
If the visa validity has already expired, the date is not actually important at all, so the third suggestion may be more appropriate