I did something similar with SNES roms. Sometimes the in-game text is encoded using "DTE compression", a mapping from one hex character to an alphanumeric seque

I did something similar with SNES roms. Sometimes the in-game text is encoded using "DTE compression", a mapping from one hex character to an alphanumeric sequence (bounded Huffman coding, basically). On certain sentences you can notice that gaps are smaller (in terms of bytes) than what should fit in there ; so you can deduce that it was a bigram (or trigram, or more).