So does it make sense? I think dateFormat itself specify exactly the output, isn't it?
If you need to parse a date you can use both at the same time:
let formater = DateFormatter()
let enDateString = "2019, 16 January"
formater.locale = Locale(identifier: "en_US")
formater.dateFormat = "yyyy, dd MMMM"
let enDate = formater.date(from: enDateString)
print(enDate) // display: Optional(2019-01-16 00:00:00 +0000)
let frDateString = "16 janvier 2019"
formater.locale = Locale(identifier: "fr_FR")
formater.dateFormat = "dd MMMM yyyy"
let frDate = formater.date(from: frDateString)
print(frDate) // display: Optional(2019-01-16 00:00:00 +0000)
Here the MMMM
pattern in the dateFormat
allows you to parse the month in plain text in the targeted locale
.