This might be a one off, i havent found enough other dungeons to tell, but when I enter the zombie dungeon this is what prints in chat:

[Player] just made the advancement betterdungeons.advancements.zombie_dungeon.title
_betterdungeons.advancements.zombiedungeon.description

Sounds like you're playing with the mod only on the server, and not on the client. You need to either install the mod on your client, or install this resource pack on the client.

Once the 1.19 version is out, the resource pack should no longer be required for clients to see the English translation