There was a small error in the code, line 1053 reads:
$txt = "##irc_group##" . $this -> bot -> core("settings") -> get("Irc", "Guildprefix") . "##end## ##irc_user##" . $data -> nick . "##end####irc_text## is known as##end## ##irc_user##". $data -> message"##end##";
and it should be
$txt = "##irc_group##" . $this -> bot -> core("settings") -> get("Irc", "Guildprefix") . "##end## ##irc_user##" . $data -> nick . "##end####irc_text## is known as##end## ##irc_user##". $data -> message."##end##";
Note the concat between $data->message and "##end##" near the end of the line.
And thanks Khalem, your fix works perfectly, no more high-ASCII chars in guildchat.