I'm sure the poster was intending that it wouldn't be complete, like English. There certainly are some letters that obey this property: DASS/DAS; S=1 BUND=BUN

I'm sure the poster was intending that it wouldn't be complete, like English. There certainly are some letters that obey this property: DASS/DAS; S=1 BUND=BUNT; D=T MANN/MAN; N=1 VIEL=FIEL; V=F VERBEN=WERBEN; V=W SIEH/SIE; H=1 GANZ=GANS; Z=S POPP/POP; P=1 That only gives five letters as the identity (H,N,P,S,Z), but that's how you'd attack it. The equivalence of D/T, for example, is unsurprising as it's an example of voicing changing; these words are in the process of changing. If you can do more complex work with bigrams, more are possible, e.g.: JAHR/JA; HR=1; HR/H; R=1