"I have three students this month."
Translation:Bu ay üç öğrencim var.
In Turkish the plural is only for an unspecified number of things. If there is an explicit quantifying word, no plural ending is necessary. So:
students = öğrenciler
three students = üç öğrenci
In a way it makes sense like this because if you already know there are exactly three of something it is just repeating yourself to say that there are more than one.