what is the difference between a load callback and list callback in the i18n hook_i18n_object_info() function?
A list callback is a callback that returns all the objects of a specific type; for example, for content types, the list callback is node_type_get_types().
A load callback is a callback that loads a single object of that specific type; for content types, the load callback is node_type_get_type().

Reference


hook_i18n_object_info()
i18n_node_i18n_object_info()