From Eggdrop Wiki
This will enable your Eggdrop with UTF-8 support.
Notice: Use at your own risk, as this may not solve all your encoding problems.
Open the eggdrop1.6.21/src/main.h file in your editor.
Search for (around line 46)
and replace it with
Open the eggdrop1.6.21/src/tcl.c file in your editor.
Search for (around line 650)
and insert the following right after it