Korean translation error

If you mean the � symbol, that usually means that the font that was used doesn’t have the character/glyph as used in the text.

The font used might depend on your device, as that is not in the stream itself.

So: on what device are you watching Apple TV+?

However, it appears from this screenshot that a part of the sentence is missing entirely.

The Korean subs show normally (I think, I can’t read it) for me at this time on the Apple TV box and Mac.

If the issue persists, then please give feedback to Apple about it, and include your TV details, so that they can try to replicate it on the same equipment.