[[Diablo]]

pawn Code:

#define MODE_NAME "Zm"
#include <YSI>

this is correct. the warning shows because the "YSI" file includes several libraries, including y_languages and y_text. those 2 libraries requires a "language" to be added to system
you can use under OnGameModeInit() callback:

pawn Code:

Langs_AddLanguage("EN", "English");
// more languages here

and the warning will disappear.