2048 ciphers requires 24 to losslessly encode 256 bits. 12 is half the security, ie 128 bits.

I looked at the options for emojis and it's less than 4096

BIP39 is based on 2048 unique 4 letter sequences, it would be hard to find a distinct 4096 symbol dictionary that has the necessary numbers. I think it would probably require 5 distinct initial characters and that is a pretty large dictionary

Codes are one of my guilty pleasures... I'd love to spend a month compiling a really good 5 letter code dictionary

It is a time consuming process though... As it is, I only have maybe 10x this total vocabulary but is about 20% foreign words