Don't treat keysyms as though they are unicode (they aren't).

src/conio/sdl_con.c

@@ -831,9 +831,8 @@ void sdl_video_event_thread(void *data)
 						sdl_add_key(sdl_get_char_code(ev.key.keysym.sym, ev.key.keysym.mod));
 					}
 					else if (!isprint(ev.key.keysym.sym)) {
-						uint8_t ch = cpchar_from_unicode_cpoint(getcodepage(), ev.key.keysym.sym, 0);
-						if (ch)
-							sdl_add_key(ch);
+						if (ev.key.keysym.sym < 127)
+							sdl_add_key(ev.key.keysym.sym);
 					}
 					break;
 				case SDL_TEXTINPUT: