str_printf is not for unicode. But you can just add the result to an unicode string with str_cat. The manual says that str_cat requires strings of the same type, but I believe it can add ASCII to Unicode - just try it.
Oh, I see. My problem is when dealing with numbers that you can't store in vars, i.e. large numbers. Currently, you can't directly print out to a unicode string. I did end up with the same solution as you suggested but this way, you need to create another string.
Thanks for the response!
