Add plugin https://dev.bukkit.org/projects/per-world-chat-plus
Isn't that plugin a bit outdated? Maybe https://www.spigotmc.org/resources/perworldserver-per-world-tablist-and-chat-1-8-1-14-3.23989/ or https://www.spigotmc.org/resources/chat-manager-1-7-1-14-with-30-features-and-40-commands.52245/ could work better, as they are updated for 1.8 - 1.14?