Cherokee

Sequoyah's syllabary, the only writing system known to have been invented by someone who could not already read.

Sequoyah finished this in 1821, having worked on it for twelve years without being able to read English or any other script. Within a few years of its adoption the Cherokee Nation had a higher literacy rate than the settlers around it, and by 1828 it had a newspaper.

This is not a cipher. It is a syllabary: each of its eighty-six characters is a whole syllable, not a letter. So it transliterates romanised Cherokee into Sequoyah’s characters rather than enciphering English. Type TSALAGI and you get ᏣᎳᎩ, three syllables and three characters - that is what the Cherokee call themselves. Type hello and you get ᎮlᎶ, because he and lo are syllables and the l in the middle is not.

The one consonant that stands alone is s, Ꮝ, which is why GAWONISGI comes out as five characters: ga-wo-ni-s-gi.

Examples:

Longest match wins, so SA is the single character Ꮜ rather than the standalone s followed by a.