How many ways can you say 15409

The number is "fifteen thousand four hundred nine".

In addition to my normal speech, I can say it in maybe ten different
regional dialects and foreign accents, but none of them really well.
I can also say it in four foreign languages that are not English.

You can "say" 15409 in potentially infinite ways:
15,000 + 409
15,001 + 408
15,002 + 407
etc.

To write 15,409 in expanded form, just take each digit and write the following ones as zeroes, adding them together like so:
10,000 + 5,000 + 400 + 9
We leave out the "00" because that doesn't have any real value.

The answer would be 10.