[15:40] recode_autodetect_utf8 = ON
[15:40] recode_fallback = CP1252
[15:40] recode = ON
[15:40] recode_out_default_charset =
[15:40] recode_transliterate = ON

You need to add rules with the /recode command:
/recode add ircnet/foo ISO-8859-15
/recode add ircnet/bar ISO-8859-1
/recode add freenode/gee ISO-8859-1

Those command will make you .speak. ISO-8859-15 on #foo on IRCNet, and ISO-8859-1 on #bar and #gee in freenode. Everywhere else you will .speak. UTF-8.