"April 20th is her birthday."
Translation:La dudeka de aprilo estas ŝia naskiĝtago.
The English translation is customised for speakers of US English, but in European countries (and in all English-speaking countries apart from the US), it is customary to put the day first, then the month, then the year. It is always "The 20th of April" or "20th of April" rather than "April 20th". Esperanto conforms to this custom.