Tough nut to crack unless it’s based on a regularized alphabet. Egyptian hieroglyphics might still be uncracked if the Rosetta Stone hadn’t provided hieroglyphics and the corresponding Hellenistic Greek and/or Demotic texts.
If I’m reading correctly, it seems to be further complicated by occasional reverse writing of the ‘letters’ and alternate lines sometimes being read in different directions (why would they do that, and what would it mean?):
https://en.wikipedia.org/wiki/Indus_script