the end notes says it all:
The letters from manga is almost identical to Hebrew Aleph-bet but only until 22nd. Also I do not see Tav (22nd Letter) or any resemblance to letter Z.
A simple hint, in Hebrew, letters also hold numbers so
from 1 to 10 , its from first to tenth aleph bet: Aleph-1, Bet-2, Gimel, Dalet, etc etc
from 10 to 100 its from eleventh to 20th aleph-bet
so if eleven, in hebrew its Yod Aleph. 12 is Yod Bet.
Welp, Devils are all derived from the Old testament so no wonder they use Hebrew letters.
Research more on your own risk.