From X-Plane SDK
XPLM_API int XPLMAppendMenuItem( XPLMMenuID inMenu, const char * inItemName, void * inItemRef, int inForceEnglish);This routine appends a new menu item to the bottom of a menu and returns its index. Pass in the menu to add the item to, the items name, and a void * ref for this item. If you pass in inForceEnglish, this menu item will be drawn using the english character set no matter what language x-plane is running in. Otherwise the menu item will be drawn localized. (An example of why you'd want to do this is for a proper name.) See XPLMUtilities for determining the current langauge.