I've seen that problem with 5.3-codex too, it didn't happen with earlier models.

Looks like some kind of encoding misalignment bug. What you're seeing is their Harmony output format (what the model actually creates). The Thai/Chinese characters are special tokens apparently being mismapped to Unicode. Their servers are supposed to notice these sequences and translate them back to API JSON but it isn't happening reliably.

I just got some interesting artifacts in Codex when I tried to oneshot a conference page design (my version of the pelican riding a bicycle).

GPT-5.4 added some weird guidance that I wouldn't normally expect to see as a normal page visitor.