erc-coding-system-precedence

erc-coding-system-precedence is a variable defined in `erc-backend.el'.
Its value is

(utf-8 undecided)

Documentation:
List of coding systems to be preferred when receiving a string from the server.
This will only be consulted if the coding system in
`erc-server-coding-system' is `undecided'.

You can customize this variable.

This variable was introduced, or its default value was changed, in version 24.1 of Emacs.