How can i rename an item that i give to a player?
and how can i give him this item in a certain slot?
Make sure you read up on Sponge’s Data API - It’s how 90% of complex data about entities, blocks and items are changed. The docs on this are here: https://docs.spongepowered.org/en/plugin/data/index.html
The method to change an item name would be, using keys, item.offer(Keys.DISPLAY_NAME, Text.of("An item"))
you need the inventory to be at least a Grid Inventory. I think this maybe explained after the inventoryAPI is implemented
Player inventories are implemented. However, other inventoriy types are not.
looking at the code, the issue will still arise if the inventory is implemented. the CarriorInventory (the inventory all entitiies give when you do entity#getInventory) and the HumanInventory (upcasted CarriorInventory for humaniod inventories) both do not implement the GridInventory, therefore setting a item into a select spot can not be done.
not to mention, this topic is about the player inventory, therefore i fail to see why you give us this information on this topic.