If I write: I was born in April 8th. Should I pronounce it as:

I was born in April eight. Or
I was born in April the eight.

I wonder if the is used here in an old-fashioned way or it's just more formal or it's not used in current English.
Born on April eighth / the eighth-- both are common, Latin. Perhaps the 'the' is more often dropped, as it slows down the communication and taxes the tongue.
As far as I know, the 'the' is only dropped in American English, not British English.