I would expect the term "digit" or "digits" more in a specific technical conversation/ documentation like a API-Interface description, not in a usual conversation or message presented to the user as a hint, error or general explanation.

It's not wrong, but highly uncommon, even when I reflect all the documentations, texts and emails i had to write to customers, technical staff or in CMS-Frontend code I had to write in customer projects.

"Number/ numbers" was always the way to go.

A different approach: numbers versus digits

digit: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 <=> these are just digits

number: 21, 567, 23471 <=> You use the digits to make numbers which represents a certain value.

For example with 6 digits you make a number with a certain value.

Compare this with the letters from the alphabet with which you make words.

Hi sandewt,
we should really not be too technical in presenting messages or anything else, when it come to "communicate" with the users.

Messages should be understandible and that begins with the right choice of terms.

Outside of technical groups I hardly had ever heard the term digit or digits for single numbers.
What's total ok internal, is confusing when it comes to explain something to the (End-)user, here the Infomessage for missing numbers in a password.

The number area on a standard keyboard is called num(ber)pad
not digitpad, the key to lock or unlock it numlock, etc.

That is, what a user can associate with, when he see such Infomessage.

Compare this with the letters from the alphabet with which you make words.

Actually, the word letter is used in sense of printing, painting..
were it's originated from in book printing letters (on to the paper) while typing on a type writer...

characters is used when to write a messages, letters, documents.

But that is nitpicking ;)

@jiweigert

we should really not be too technical in presenting messages or anything else, when it come to "communicate" with the users.

Indeed, the following could be an intermediate solution:

This language string:
JFIELD_PASSWORD_NOT_ENOUGH_INTEGERS_N_1="Password does not have enough numbers. At least 1 number is required."

Could be:
JFIELD_PASSWORD_NOT_ENOUGH_INTEGERS_N_1="Password does not have enough numbers. At least 1 digit is required."

Digit is the correct term. But I'm not going to argue with native English speakers. My only wish is that a note is added for language translators so they know it should be correctly translated as digit.

I agree with Brian in this case. numbers is the phrase used most at least in British english.

@wilsonge You just killed #30559 as these strings are useless in installation...

Thanks @wilsonge